Last night, after a fun (yes, I used the "F" word) and productive day of editing, it occurred to me that:
a) V12 hasn't crashed or froze in a couple of weeks, and
b) I'm getting the best timeline playback that I've experienced with any version of Vegas, even with masks, CC, and track motion.

I've been editing since the bad old days of video and have used some amazingly poor editing systems, so I've never been more than mildly annoyed by Vegas crashes; I save after every couple of edits and have never lost any work. My major issue has always been poor timeline performance... Low res preview, low framerate, video edits out of sync with music and narration. These things have made editing very tedious and very frustrating, especially when pulling an all-nighter.

These issues are largely gone (framerate still drops with track motion) and I wanted to post my experience for those who may be having issues with V12.

System: Work (specs are posted and up to date)
Version: V12 (394)
GPU: Acceleration OFF
Notes: Increased available RAM to 2048MB as noted in this thread (this has made the biggest difference, BIG THANKS to megabit for the tip!): http://www.sonycreativesoftware.com/forums/ShowMessage.asp?MessageID=839151&Replies=30