Since downloading 1.2 via Steam tonight, I've experienced an immediate crash to desktop on startup of NV after selecting "Play Game" from the launch menu. I solved it by removing ArchiveInvalidationInvalidated! mod, which I downloaded from NV Nexus. Doing so allowed me to launch the game and play.
This is unfortunate, because it was one helluva useful mod. If there is a version of it out there that does not kill 1.2, please point it out.
Meanwhile, back to the stone age of messing around with ArchiveInvalidation.txt.
The 1.2 patch screwed me over. Click play and the game instantly caused an app exception (thanks for that Obsidian guys). Remive archive invalidation, and the problem remained, although it took about half a second longer to get the app exception. Went into steam client, library, right clicked on New Vegas, under games, brought up properties, selected the local files tab, clicked the Verify Integrity of Game Cache button. The steam client confirmed that there were 625 files that were different and then proceded to download about 1GB worth of content.
Seems to be working now, though.
Will reinstall AII now and see if it still works.