Yes, I would be concerned about that too- and I can imagine that at least for the boot drive they would not be the best choice out there when there are so many other fast high capacity drives available. For data drives I am sure they are fine, but the failure rate would concern me- I did not read many of the reviews but I did see that in some I read.
Personally I could not be happier with my Samsumg Spinpoint F1 drives in my Mac Pro. Very quiet and among the fastest large capacity drives out there- which is why I have three 1Tb and one 750Gb in my MP!
Just a side note on purchasing- a lot of people (me included) love dealing with newegg and OWC because of their rock solid customer support and good pricing- and as you know, that is not always a given with eBay sellers- but hey, that is your choice of course!
On the RAID question- after a few bad experiences with RAIDS (both hardware and with Apple RAID 2.0) I have shied far away from them personally. Keep in mind that a mirrored RAID still only provides partial safety, and in
no way should they be considered as a substitute for a real backup. For example should you delete a file accidentally it is instantly gone from both with no backup to retrieve it from. The same holds true if a program goes amok and writes bad data to your drive. Depending on what is written and where it is written it could spell the end for both the mirrored drives in a flash with nothing, again, to restore from. Tools like Disk Warrior are not written to deal with RAID arrays (although possibly they could work with mirrored arrays, but I have my doubts).
My approach to that is to buy some of the fastest individual drives I can get, and only use RAID if there is a specific need for it as would be the case in some areas of professional video editing/rendering. I really think there are a lot of people out there who are seduced by just wanting the highest speed specification and are not aware of (or choose to ignore

) the potential safety costs of RAIDs honestly.
I can't really comment specifically on speed differences between cards and Apple's latest 2.0 version of Software RAID since it was awhile inbetween the times I used them, but suffice it to say that the hardware RAIDs were certainly faster.