Is it worth it for me to start mining with Deepbit if the best videocard in my studio is an old 9800gt, especially given that I can't run it 24/7 since I use it to test our OpenGL projects? Would I be better off just buying the Bitcoins?
So I might have an answer for you. I've been using a dedicated mining rig with deepbit for a little over a week now. So far it seems totally solid, I can set automatic payouts and such, that's all fine. The machine I'm using is basically my old gaming PC. I's a low end core2 duo, with an nvidia 9600 GT - all and all a pretty lackluster machine. I decided that since It would be my only expenditure, I could pick up a radeon 6950 as a second video card, turning it into a real mining rig.
The overclocked radeon puts out 350 Mhash, while the nvidia card sits there doing nothing. I've gotten about 10 Mhash out of the 9600 GT, and about 38 Mhash from the 9800 GTX+. With a 9800 GT, you can expect to be between those, probably about 30 Mhash. All and all, I'm not entirely sure the nvidia cards are worth the electric bill. I actually decided to swap out the 9800 gtx+ card i had in my rig, in favor of the 9600 gt just because of power consumption. Also, this way I could have the radeon dedicated solely to bitcoin, with 9600gt handling actual video needs (now it's a bitcoin rig & media-center PC).
As far as buying goes, watch the market, it seems to be dipping, which is actually a good thing if you want to buy. The technology is proven, it works. just wait, that price will come back up and in the mean time, you can get more coins for your dollar. I think buying is the way to go.