Invest in a SCSI or SAS adapter and go with those. Buy a small "new" Maxtor, cause they are Seagates, as your OS drive and put everything else on SCSI. They last forever and have minimum failures in comparison to 3.5" or 2.5". New WD Raptors are catching heat for using 2.5" platters but SCSI has been doing it for a long time and they are faster and more reliable, though the new Raptor is crap IMO. I've already had 3 in, in less than a year of the new models. All conspiracy talk here is true. Companys know an "average" lifespan or hours for a drive and they will exploit it. Seagate while a good drive is no exception.
http://www.fluffles.net/articles/seagate-AAK-firmware - An example of making things better or worse by luck of the draw in a store where you can't check the firmware of the drive before buying. I haven't confirmed any of the reports on this site but imagine it could hold some merit.
IMO put all of your most important data on a SCSI/SAS drive and then put all of your other "crap" on a giant, cheap Seagate because they've got the best warranty. I am by no means saying that SCSI drives never fail but look at their lifespans or Median Hours compared to a consumer desktop drive and what they are built to do versus a desktop. I think the underlying issue is that hard drives usage have grown so fast as far consumers using them "harder" and more often than companies data in the past has shown them. SCSI drives are built to be ran for years without stop and consumer hard drives are built to be cheap and in hopes that the consumer will get a "better" computer before the Median Hour point is reached.
"I can get a good look at a T-bone by sticking my head up a bull's ass, but I'd rather take a butcher's word for it."