Funny. My original like day-one MacBook had a 60GB Fujitsu in it. Within a couple months I replaced it with a 100GB Seagate. Which failed in a hurry, and Seagate replaced it under warranty. What I read at the time was that the firmware in those Seagate drives didn't get along with MacBooks. My replacement unit from Seagate was the same model drive but had updated firmware. It's worked like a champ for more than three years. The 60GB Fujitsu, the original MacBook part, is still working just fine in a $14 external USB enclosure.
The 80GB Samsung in my rev. A MacBook Air has been beeping and clicking for at least 18 months of the two years I've had the Air. But not a hint of failure, no read or write errors, no data loss or corrupted data, no boot fails, no lockups. I gambled and didn't buy AppleCare on the Air. Made it 12 months out of warranty so now the price of fixing the HDD if it does quit within the last 12 months AppleCare would have covered will be less than price of AppleCare would have been.
Last time I checked into the Air HDD issue, there seemed to be debate in the Air community about whether the noise was precursor to head failure or a noisy a head-locking mechanism and/or spin-up process. It's the same drive series as was used in many HDD iPods. A fair number of those HDD iPod owners reported the exact same noises emanating from their iPod drives; a few reported their iPods had eventually tanked, but the majority reported their noisy iPod drives were still going strong after years of daily use, regular writing lots of data via syncing, etc.
Leads me to believe it's difficult to determine from HDD noises what is a precursor to failure and what is weird and perhaps out of spec but will never actually fail. This is of course why I do the Time Machine thing.
(I should add: The Seagate in the MacBook that failed on me, it never did anything peculiar at all until one day while using the MacBook, the laptop locked up and then couldn't ever find the drive again when I forced a few restarts; no Apple or 3rd party drive utility software booted from the DVD drive could see it, either. It just went bye bye.)