[Megan]

I don't know if a plugin exists but I feel like it would really help if you could start typing someone to tag them and it then gives you options for the username? It'd certainly help prevent mistaggings.

[mothered]

I certainly agree with this suggestion.

Aside from other benefits, sometimes you may not know the exactness of the username (such as referencing a new member), and the autocomplete feature would be of big help.