I knew it was going to coincide with SMP, but what I didn't know was whether it was the initial public release of SMP, or after it's finished and polished up, or what.
I see the following on the official blog:
I will release the SMP server before I leave for that. It might be buggy, but I promise to fix it when I get back. It will be missing mobs. Mobs will come later on, and when they’re in, the game will officially be in beta, and the price will go up to 14.95 euro.
as well as this:
August 30: Back to work, finishing up survival mode multiplayer. Enemies will probably get added around here.
So enemies in SMP seems to be the cutoff point for the beta, and that's scheduled for August 30.