In the latest snapshot post, Jeb hopes to have the 1.4.6 pre-release out by next week (maybe). 1.5 won't be out until early next year.
BTW, you can download the current 1.4.6 snapshot (12w50b) from http://www.mojang.com and run it by replacing minecraft.jar with the one you downloaded. MAKE SURE TO BACK UP YOUR OLD ONE FIRST!!!! Then, if you want, you can switch between them as you please.
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Quote from Albert Einstein »
There are two things that are infinite: the Universe and Human stupidity. And I'm not so sure about the Universe.
In future if you want to keep up with the news and release dates on every minecraft version that's coming out, follow those steps:
Step 1. Follow Jens Bergenste and Nathan Adams on twiter.
Step 2. Bbookmark MOJANG Blog and THIS WiKi page.
Step 3. (Optional) if you are using Google Chrome, download THIS button for easy access to your Twitter