So add it!
SOUNDEX doesn't cover, particularly, the typos angle that Bill seems to have concentrated on. Probably a lot better for the search results, given its sometimes 'strange' output.
Seriously though, if you incorporated this with some Ajax, and used that for dynamic spelling correction, like Word does, it would be very nifty.
I recently built an Ajax menu that works on the very simple concept of 'update as you type'. Given folks' ability for typos and fat-finger, this might just get added to second-guess them.