Casascius gets it. Paid 0.3BTC to 1BowSerbsenLBELbwR5aZE1aqy7ooGCydT (firstbits under his prof. pic).
Thanks everyone for your enthusiasm. That was shockingly fast!
Anyone know why all p2pool blocks seems to start with the payout address "Unknown: 0"? Perhaps people mining without adding any payout address?
Looking at the block, it looks like something is intentionally being shoved in the coinbase for some other purpose. The size of the data looks like it's possibly a hash of something else, but otherwise it is an unredeemable transaction with a value of zero.
My guess, based on how I understand p2pool works, is it is likely the hash of the most recent block in the share chain, since the same block that makes it into Bitcoin also becomes a block in the share chain.