In reply to Robert Cartman.

It's actually been built to be pretty sensible about this sort of thing, though time will tell if we need to tweak things.

For example, if you have the Friends component enabled, it pre-caches the list of all your friends when you load any page (that supports @mentions). Then, when you hit up a @mention, it searches in your friends list first, and only connects to back to your server if a match isn't found.