I think the 512 difficulty is too much for CPU mining. I ran cpuminer on 3 cores of my machine (33 kh/s total) and got work submitted after 21 mins.
You may want to look at mining Primecoin (XPM). This is where I put my CPU to work:
http://www.peercointalk.org/index.php?topic=485.0This simply isn't true. CPU mining is perfectly viable at 512 share difficulty. Share difficulty DOES NOT MATTER - it only increases variance.
It sounds to me like his stratum proxy is lagging - try pointing the miners direct to the pool and see what happens.
I was really hoping that it was the stratum proxy lagging, as I hadn't checked that before, but my tests show a 50ms delay from miner to stratum proxy to external proxy to Wafflepool. I'm not sure that that kind of delay is enough to cause this issue though. When I was mining Litecoins before I switched to this pool, I was always getting a difficulty < 200. Any time it went above 300, I started to have the issue of less accepted shares because of the time it takes the cpu to calculate such a high difficulty share. If you say CPU mining is perfectly viable at 512 share difficulty, then I'll keep working on my config to see where my setup is going wrong. I am really hoping to be able to stay at Wafflepool. Thanks for the info.