Apparently using freshly-generated coins too in some cases, e.g. this payment http://blockchain.info/tx-index/16885882/c2d0742df8df67c0507fd270b3c262f8a0118ba3a9b91357c83a04d952d0a32d - very interesting.

Edit: not just freshly-generated coins that weren't mined by any pool that blockchain.info is aware of, but ones that were mined with a very unusual 47.5 BTC / 2.5 BTC split in the coinbase payout, which means custom software.

Edit 2: and yep, that entire payment comes from coinbase transactions paid to http://blockchain.info/address/1PSf86KnLuzM7Ris5kDhTEZwooR3p2iyfV - which represents 5+% percent of the total Bitcoin hashpower right now at a quick estimate. I have a bad feeling about this.