I keep my MB toons and my solo toons separate.

I really hate changing my UI, keybinds and everything else in between the 2. When I'm multiboxing I'll use a completely different set of keybinds(and obviously macros) than when I solo play. I raid on a resto druid and multibox my toons. Outside of raids I probably multibox more than I play my solo characters, and when I'm leveling professions, etc I won't always log on all the characters at the same time(call me crazy).