In general, auto-save is fast and unobtrusive. For larger projects (I'm currently working on a file with 110,000 segments) however, the process can take a minute or longer. This is made even more frustrating when autosave starts when I'm three letters in to typing a word.
Having the autosave function start checking at the set interval and then waiting for a keyboard pause of even 5-10 seconds before beginning would at least keep it from interrupting while the words are flowing.