\Anybody using a MBA as a primary computer?
Yes! I absolutely love my 11" MBA. It is my primary computer and I don't feel like I am missing anything. Why? Because it isn't a Dell hacintosh netbook using an Atom processor.
The only reason(s) a reasonable person wouldn't want to buy one:
1. You're a crazy, hardcore gamer.
2. You produce more than you consume (film making, music making) and you're not patient enough to let the processor do its work.
3. You have a phobia of external monitors.
4. You have a phobia of external hard drives.
5. You have a phobia of desktop speakers.
I am sure other users can add to this list. The bottom line? You know what you need. Are you a power/pro user or are you not? If not, do you plan on becoming a power/pro user in the future? If yes, do you feel as though you won't be able to buy an iMac or something to complement your ultraportable Air? (Note: I see the OP has an iMac. I am thinking mainly about users, asking the same question, who don't.)
Perhaps someone can make an (objective) decision flow chart to end all of these threads. That would be cool.