Looks like your key focus is quality of review. I'm thinking back to the days where FTP sites had "points" that you acquire by uploading files, which you could then redeem for downloading files. Perhaps a similar idea could be employed in this case. You earn points by reviewing sessions, thereby allowing you to post sessions of your own. You would probably have to award points based on the size of the session you are reviewing.

Mandatory things for ease of use:
<ul type="square">[*] Every hand converted and posted according to the standards listed on 2+2[*] Reads provided automatically, if available[*] Anonymity[/list]

I briefly read over some of the other ideas in this thread. To the OP: simplicity is key. I'm a software engineer, so I might be interested in drafting some hard requirements and coming up with a solid design. I may or may not have time to dedicate, but PM me if you'd like.

Some more ideas:
One conern I noted is that players may be concerned with who is reviewing their sessions. Similarly to how these forums have a post count, this app could offer a count of how many hands an individual has reviewed. Additionally, players could provide their own stats. You may also want to include some sort of method for reviewees to contact reviewers. It may also help to provide random sessions to be assigned to reviewers.