I got it too, but ended up rolling back to 0.123 after having a ton of hard-locks.
I've actually been having quite a bit of instability with the recent builds and thumbnail building again, particularly since the new mini-thumbs were added to Theater View. It's random, but I'm seeing quite a few hard-locks (where I have to kill the process manually), and I'll see multiple copies of JRThumb.exe open but not using any CPU in Process Explorer.
Unfortunately, I've not been able to track it down to any particular reproducible "action" that will cause it. Simply selecting files (not playing or anything, just choosing files) seems to completely lock it occasionally. When it locks, the UI completely freezes (I often wait 5-10 minutes to make sure), but the Media Center 12.exe process isn't using any CPU... Just seems stalled.
Killing the process and repeating the same action that "caused" the lock never repeats it though, so I've been at a loss to help on it. Generally, this seems worst when new media has been added to my library, so I'm guessing it's thumbnail-building related again. That's just a guess though, based on often seeing JRThumb.exe in Process Explorer as (or just before) it happens (I certainly haven't checked every time though).