Vegas 12 is more stable than previous versions in complex projects. I use it a lot.
I only see 3 problems:
1. Vegas 12 doesn’t detect my Blackmagic Design Decklink card as the preview device. (I can preview in a TV connected to that card in Vegas 9, 10 and 11 in the same PC).
2. In previous versions I was able to edit a photoshop file inserted in vegas time line, and I was able to see in Vegas the changes saved in Photoshop without closing Vegas file. In Vegas 12 I can’t do that. Photoshop files inserted in the time line becomes locked until I close Vegas application.
3. Newblue Titler Pro still doesn’t work. Vegas crashes right after Newblue Titler is dropped into the time line.