gdgt

That is a somewhat open ended question, and the answer is largely dependent on how you use the drive. Hard drives are easily one of the most complex devices in and around your computer, with all manner of moving parts inside.

If you find yourself performing lots of writing to and reading from a drive, you can expect your mileage with that drive to shorten. As a general rule I would expect the average hard drive to last about 4-5 years. Some will last longer, and some will break sooner, but there's not really a hard and fast answer to 'when'.

That's why a multi faceted backup solution is so critical. Your hard drive WILL fail. But no one knows when. As a good rule, check it periodically with diagnostic software. Bad sectors are not too big a deal until they start happening more frequently. That's usually a sign that your drive is on the decline.

If you are only using it as a backup and if you have been handling it with kid gloves, then it should be good for years. However, if you are the worrying kind, you could check the drive with a low level diagnostic utility - if you can find one that works over USB/FireWire - most can only really do their magic over SATA. Since you have a LaCie, I am assuming that you can't self-service the drive (i.e. remove it from the enclosure).

You could always open a savings account for emergency repairs and for you next computer. Drop in enough money every paycheck to replace your computer every two or three years (or whatever your upgrade cycle is), and you are prepared. Small incidental repairs will delay the purchase of that new computer by weeks or months at the very worst.