Just to report to the community on my WD 640 Gb experience.
Long intro (skip, unless nothing better to do): a 2nd 500 Gb 5400 Hitachi died on me in 4 months. I asked for forum advice and decided to try installing a "better" drive to see if it will survive my ways of handling a laptop.
I bought a WD 640 Gb Scorio Blue from Microcenter for $140 + tax. Istalled without a problem and used a TimeCapsule to restore my previous machine. It took > 4 hrs using a network cable. Don't know how long for sure since I fell asleep. In the morning I found the machine restored successfully and itwas working well.
So far, I haven't noticed any issues other people have been reporting with their WD drives (stuttering, beachballing etc.)
Noise: overall the drive is much more quite than a Hitachi. It's baseline noise is a fan-like sound that someone on this forum described as a "whooshing" sound. I don't have a musical hearing and I can only hear it with my ear within 1-2 cm from computer. Hitachi drive had a lot of clicking/tin like sounds that were quite noticeable, and these are gone. Occasionally it does click when idling (someone here said it was the heads being moved to save energy) but the sound is low-pitched and muffled.
When compared with my sister's MBP 13 with a Seagate 7200 320 Gb, the WD drive is subjectively a bit more quiet with possibly less vibration, but I obviously haven't done any measurements.
Overall, it's not a completely silent drive, but I personally like it's repertoire better than Hitachi's.
------end of main post, everyting written after that is not meant to be taken seriously---------
Genius experience -- I did take the machine to the Genius Land yestrday and had the following dialogue with one of them geniuses:
ME: Hello, my hard drive broke. Again. [made a sad & begging face] Can something be done? I tried to run the Disk Utility but to no avail.... Please-please
save my computer [sob]
: Well, of course, don't be such a cry baby
let's have a look... [runs DiskUtility and some other program, nothing seems to work]. Well your computer is obviously not working, but it's because the file clusters interference with string theory partitions were collapsed cause irrecoverable cross-referencing of indexing system. You need to go home & re-install the OS, or we do it for you if you leave the machine with us & still go home.
ME [not liking the proposal that I go home without computer]:
but Sir, I don't think the system will install on a bad drive. Do you mind getting the disk utility to OK the drive, then I will gladly go home to re-install the OS myself.
hmmm, well [trying to accomplish that unsuccessfully] but even if I gave you a new drive, since this is the 2nd drive that fails in just 3 months I suspect that the backup that you have on your Time Capsule contains some
errors that if transferred to the new drive will damage it as well
. [This could only have come from a genius: a software bug containing some evil kill sequence that akin to a deadly virus destroys one hard drive after another]
ME [making a serous face, trying to look like the main protagonist of the Hitman game]: I do not agree with you. My computer is not working! Do something that it starts working. Or else
[I really didn't say "or else" but I was trying to tune in to his brain frequency & transmit this threat telepathically, unfortunately he was either wearing a metallized besaball-hat or having no encephalus rendering him immune to my telepathy hacks]
[looking disiterested and trying to help a second customer that was brought to him by a receptionist]: Aha.... I see now.... now I got it figured out [I became very worried when I heard that] We will replace your logic board. [he probably noticed me becoming pale and decided to soften the blow] But don't worry it will be free of charge to you
ME [reaching into my jacket pocket for the nitroglycerin pills]: How long?
Probably around 5 days or so 
ME [with strong russian accent]: give back my computer!
BTW -That poor fellow added to our duo by the receptionist (maybe to make me realize my time was up) needed an optical drive replacement and they also wanted him to leave the computer with them for 5 days!!! I overheard them say that the parts needed to be ordered. Why can't they stock some commonly used parts is a mystery to me. They work on Macs only, there aren't that many parts to stock, right?
The customer asked them to order the part and call him when it was in. It was supposed to reduce the time the computer had to stay with Genius to 2 days.
Why, why does it have to take such a long time to replace an optical drive? I middle school pupil could be taught to do that in a couple of hours
Truly the Genius Bar - you have to be a genius to work there.
Long intro (skip, unless nothing better to do): a 2nd 500 Gb 5400 Hitachi died on me in 4 months. I asked for forum advice and decided to try installing a "better" drive to see if it will survive my ways of handling a laptop.
I bought a WD 640 Gb Scorio Blue from Microcenter for $140 + tax. Istalled without a problem and used a TimeCapsule to restore my previous machine. It took > 4 hrs using a network cable. Don't know how long for sure since I fell asleep. In the morning I found the machine restored successfully and itwas working well.
So far, I haven't noticed any issues other people have been reporting with their WD drives (stuttering, beachballing etc.)
Noise: overall the drive is much more quite than a Hitachi. It's baseline noise is a fan-like sound that someone on this forum described as a "whooshing" sound. I don't have a musical hearing and I can only hear it with my ear within 1-2 cm from computer. Hitachi drive had a lot of clicking/tin like sounds that were quite noticeable, and these are gone. Occasionally it does click when idling (someone here said it was the heads being moved to save energy) but the sound is low-pitched and muffled.
When compared with my sister's MBP 13 with a Seagate 7200 320 Gb, the WD drive is subjectively a bit more quiet with possibly less vibration, but I obviously haven't done any measurements.
Overall, it's not a completely silent drive, but I personally like it's repertoire better than Hitachi's.
------end of main post, everyting written after that is not meant to be taken seriously---------
Genius experience -- I did take the machine to the Genius Land yestrday and had the following dialogue with one of them geniuses:
ME: Hello, my hard drive broke. Again. [made a sad & begging face] Can something be done? I tried to run the Disk Utility but to no avail.... Please-please

ME [not liking the proposal that I go home without computer]:

errors that if transferred to the new drive will damage it as well
. [This could only have come from a genius: a software bug containing some evil kill sequence that akin to a deadly virus destroys one hard drive after another]
ME [making a serous face, trying to look like the main protagonist of the Hitman game]: I do not agree with you. My computer is not working! Do something that it starts working. Or else

ME [reaching into my jacket pocket for the nitroglycerin pills]: How long?

ME [with strong russian accent]: give back my computer!
BTW -That poor fellow added to our duo by the receptionist (maybe to make me realize my time was up) needed an optical drive replacement and they also wanted him to leave the computer with them for 5 days!!! I overheard them say that the parts needed to be ordered. Why can't they stock some commonly used parts is a mystery to me. They work on Macs only, there aren't that many parts to stock, right?
The customer asked them to order the part and call him when it was in. It was supposed to reduce the time the computer had to stay with Genius to 2 days.
Why, why does it have to take such a long time to replace an optical drive? I middle school pupil could be taught to do that in a couple of hours