Last bit of enhancements were added to the mentioning capabilities:
1 - Manual mentions will now be color-coded (same as the ones picked off the drop-down)
2 - Mentioned usernames will now link to the users profile
3 - If you do a manual mention and preview your post, the color coding and linking will happen so you can tell whether you did it correctly
I can't think of anything else that needs to be done for this functionality, but if I'm missing something (or something isn't working the way I said it should), let me know right here in this thread...