So I got my 5870 yesterday and I've had it going in Deepbit for a day (Previously had a 560Ti, just wasn't cutting it).
After reading the anti-Deepbit threads I've decided to try it alone for a month. I've just ordered another 5870 to double my hashing power and at current difficulty levels, calculators tell me it'll take 10 days on average to generate my first block.
How do I know that I've not done something wrong? Poclbm is happily mining away with a speed of 370mhash/s so I assume it's doing something. With Deepbit I knew it was working because I could see the results by the hour, but how do I know this is working?
If you're seeing numbers (eg. 370mhash/s), then it's working.
It should show you if there are any invalid blocks that would cause you issues.