A quick reminder to myself. I'd been having an issue where Vim was running very slowly on an index.html file in insert mode. After a quick google came across this SO post which shows how to debug such issues. In my case it was omnicompletion that was causing the delay. A quick update of my plugins (:NeoBundleUpdate in my case) solved the issue.
:profile start profile.log :profile func * :profile file * " At this point do slow actions " go to a script tag enter insert mode :profile pause :noautocmd qall!