I have been running mine for about 3 months non-stop as a web server for www.sm0vpo.com where there are about 10,000 electronic PDF files and about 250 electronic projects that i have fully documented with PCB poil patters in ZIP and GIF form.
I have about 3,000,000 hits per year so my little RPi will have seen about 700,000 hits as well as experiencig both heavy and light traffic.
I have the RPi running "barefoot" (no keyboard, monitor or mouse) with no external USB connections. The only connections are SD-card (SanDisk EXTREME 8GB @33Mb/s). I reasoned that the keyboard, mouse and memory stick could burn as much as the RPi itself.
The RPi has never once crashed, is slightly warm and I consider it to be 100% reliable. An MS Windoze-XP machine running the same traffic had to be restarted about every second month on average, with a lower traffic density. The RPI is also faster than the 2.66GHz HP computer but I believe this to be a function of the different operating system (my RPi is running LINUX - debian).
If you want more information I can send you pictures, but at the moment and as a newbie, I cannot access net logs in the lighthttpd server. If you have any command sequences I can enter into my SSH terminal then you are more than welcome to share all information (and softare) I have.
FYI - My RPi is hidden behind an IP-Cop (LINUX) hardware-dedicated firewall, but I hope one day to change that ATX card for a dedicated RPi server/firewall. I am only missing one component - time.