Antminer S3 is P2Pool Compatible as per their update in the second post of another thread.
Please quote the source where they state that.
Nowhere do they say the S3
is compatible with p2pool (or the S2 for that matter) - only that it
will be compatible. I would rather buy hardware that
is compatible - not that
might be sometime in the future, maybe.
Peace

Reserved for Q&A and Updates
1. Will there be upgrade parts for S1 and S2?
Yes, there will be. But we still need to solve some production/testing problem before we finalize the plan and public it.
2. Will S3 be supporting P2pool?
Yes.
Updates:
1. The sales opening announcement and the final specs of S3:
https://bitcointalk.org/index.php?topic=656461.msg7597300#msg75973002. The First Batch of AntMiner S3 runs out of stock. we are ready to start to sell the Second Batch of S3 at 22:00 pm on July 1st (UTM + 8 ), and drop the sales price to 0.74 BTC each with international shipping. The Second Batch is estimated to be delivered about 2-4 days after shipping of the First Batch of S3 for 0.75 BTC each, but still no later than July 20th.
3. The Third Batch of S3 sales price is dropped to 0.725 BTC each with international shipping, which will open sales at 22:00 pm on July 4th (UTM + 8 ). The Third Batch is most likely to be shipped before July 20th, but no more than one or two days delay may happen.