Specs for my Maxtor DX541 and my WD both say "minimum 5 years" and "minimum 50,000 start/stop cycles". To say these drives get hard use is understating the issue; I've never had a problem with either with my box running about 16 hours a day. The Maxtor I migrated from my old DEC box; it's going on 5 years without a single problem.
Tom