Great. A Block! I also sent some BTC using sendmany.
Thank you for the 0.39755 mBTC!

Although the block only has 2 transactions
I suppose that's better than the previous block, which only had 1 (the coinbase one)
I just joined P2Pool on 4/5/15 and am pretty pleased.
How do we determine the address corresponding to the person in the P2Pool who actually mined this block so we can thank him/her directly?

No, it had lots of transactions.
If it only had 1 transaction it would be pretty much as bad for bitcoin as the last one.
As for thanking them ... well it is completely random finding a block ... and they get thanked by getting a block finder reward by getting a small % of everyone's expected payout from everyone mining on p2pool

You looking at something different than I am? Last block found by p2pool was 352654, and that block had only 2 transactions, of which the generation transaction was one... so it's almost just as bad as the last one