Downloaded, attempted to play, discovered it segfaults just about any time I try to actually do anything (e.g. start the tutorial, join a match, practice with bots, change video or audio settings...).

I can definitely see why this is still only in testing right now, it doesn't appear to be ready for prime-time at all yet.

Apparently I'm not the only one getting segfaults all the time though, so I'm adding my experiences and information to the existing bug (https://github.com/ValveSoftware/Dota-2/issues/142, in case anyone else runs into the same issue), hopefully they'll figure out what's going on and get it fixed.