Mojang have just recently released a new snapshot for Minecraft 1.3: 12w30e. Originally, Mojang released a 12w30c snapshot, but that came with a frustrating bug I heard, and then after that they released a snaphshot 12w30d to fix that bug, which in turn introduced a new bug which allowed duplicating items from the hotbar into the creative mode survival inventory.

Then they released 12w30e: to fix that dupe. Which in turn brought a new bug into the game: sometimes being unable to equip plate bodies whilst in the survival inventory in creative mode (I found this bug very annoying).

Now, aside form the bugs, not many features were added in these snapshots. The most popular feature seems to be the change to log blocks. Their placement position depends on where you're standing.

Here is the link from the Minecraft Forums: 12w30e Ready For Testing - Pre-Release Tomorrow; MineTV Debut - News - Minecraft Forum