I use @thunderbird at work and on the whole it's great but one thing I would appreciate is if the status bar at the bottom of the window could be more indicative of, you know, status.

After starting up it quickly changes from a progress bar to a generic "downloading message ..." with a spinner animation. How many messages? Which one are you on? Maybe it can't give a time estimate but surely if it's working through a list it could say "Downloading message 1 of 25" or similar.