With Minecraft update 1.3 "getting closer", Mojang has released the snapshot a day early. Today's patch is technically snapshot 12w26a. Earlier today, Minecraft lead developer Jens Bergensten confirmed that the fate of the 1.3 patch will likely be determined on this snapshot.
As such, today's snapshot has a very simple change log that consists of general bug fixes. Jens didn't get into specifics, but did say that one big performance bug was found and fixed as well as a lot of smaller ones.
"We still need to test more before it's ready," he said.
Last week, Jens gave a little info about what has been holding back the 1.3 patch.
"The biggest problem right now is that since the game is hosting a server in the background, the game requires more hardware resources than before," he explained. "We're trying to figure out a way to solve that."
It's unclear if that was the big fix or if they are still attempting to solve that problem. In the meantime, you can download the latest snapshot for Minecraft and attempt to find any more bugs.
You can find the Minecraft shapshot for week 26 here: