I don't know how long I've been using my WRT54GL, but it's got to be at least 7 years - always running Tomato firmware. 24/7. For the first 4 years wired+wifi and for the last 3, wired routing only (turned off wifi). For the past 3.5 years I've been using an Apple Time Machine for WiFi access 24/7. No issues with either product.

That said, this WRT54GL was a replacement for an original WRT54G that died after a couple of years.