Mine has been running for 4 years being switched on and off about eight times every day. Both ways work equally as well, it's just the added fire risk you need to worry about, not doing damage to the PC.
I have left my pc on for the last few months and it runs fine. I have been told many times by pc engineers that it is better to just leave it on and just set your monitor to turn off after 10 mins of inactivity and my two hard drives are set to turn off after an hour of inactivity.
This has confused me a bit. I thought win98 suffered memory management problems if left on too long? If I ran large games for example on my old 98 pc, I would have to eventually reboot to de-segment the memory?