Invitation to Review Conference Proposals: Pros and Cons? WWTFD?

[Vkw10]

I just finished scoring proposals for a large national conference. I had a dozen to score, four items to rank 1-5, and a comment field. Took about two hours. No compensation. For that conference, two people score each proposal online, the top scored papers in each conference thread fill about 95% of the spots, then the program committee looks at proposals with wildly divergent scores and proposals that didn't quite make the cutoff score and fills in the final spots. The program committee bit is time consuming, because they're trying to balance the program; reviewing is quick.