The obvious is be productive and check email, Twitter, and Facebook. Done.
The next: Stream audio... Maybe suggest the Pandora Radio App? Perhaps Mouse World Radio or Live 365 for some Magical Mouse Radio? Done.
The not so obvious:
Use Google Voice to send text messages. You can't talk, but you can text to any US number while in flight!
Tweet about your flight progress. It will either annoy everyone, or be a great way to let the awesome person picking you up about your progress :-)
Play online games like Words with Friends. I am getting spanked in most of the games I am playing, but at least it's fun!
All this just to pass the time until I land and get an awesome hug from Erin when I see her at the airport... Today it's the destination, not as much the journey.
How about you? What do you do while inflight?