p2pool: Is it setup correctly? "???" in efficiency
You won't see a value there until you mine a share, so seeing a ??? is normal for the moment. The efficiency is a measure of how many shares have been counted in the share chain verses the ones you have found. 

At 2GH/s you should be expecting to see a share soon, given an average of 2 days 8 hours to find a share at 2GH/s at difficulty 88800 (the current for p2pool).