Yeah, I highly recommend overclocking as long as you have the right hardware. Its a great way to get a bit more for your buck.

I run my c600 @ 900mhz and my Geforce 2 GTS at 250/400mhz (from 200/333), well above spec on both counts, and overall a huge performance increase.

Good luck, and if you tell me what card you have, I can recommend the best software to overclock it with.