At least building one myself, I only have to buy the parts that I need. :) And I didn't have to transfer my files from one hard drive to a new one. The motherboard came with a 1-year warranty. I've had the system since August 2001. How long are the manufacturers' warranties? I don't do the extended ones. :) If the HD went bad, I'd just buy another one from Seagate or whomever and put it in myself anyway.
I think Dell's standard is three years. And it's worth it - usually they'll ship you the part overnight, no questions asked. I likee.