UGH. I recently forked technomancy's emacs-starter-kit, and all was well, until I started editing erb files. After a while, it would stutter (hang and then go), eating up 94% cpu while editing erb files. I didn't know exactly what was causing it. Emacs kept complaining about "MU new post-command chunk" in the *Message* buffer, and something about "not safe forward word". It took a whole night's worth of digging to figure this out.
Solution: make sure you upgrade to the latest version of nXhtml (2.05-091202), if you forked technomancy's emacs-starter-kit commit 452c395556e0aac213b0d7d1653f2673554a4b73 or earlier
Sometimes, I hate emacs.