Autocomplete for tags

Tags are tricky-- should they be plural? How granular should they be? How generic should they be?

I think something that could help solve this problem is autocomplete suggestions while typing out tags. As I've been looking at posts and retagging, I've realized a lot are placed in single-post tags. Sure, this is bound to happen, especially on a new site, but autocompleting tags as you type them should help encourage users to tag with the correct one, like academic studies vs academic study.

The main con I can see with such a system would be overtagging. Since tags should actually apply to the topic at hand directly, seeing these tag suggestions could encourage people to use less applicable tags rather than think of them themselves.

Thoughts?