>What bugs me the most so far is that the messages are too small.

A Big, I'll second that! When you get as old and gray as me your eyes are not as good. It should be simple enough to allow users to select font sizes for both the thread list and message frames. This default info would be stored into the user profile. It would be nice to set a percentage of how much the top thread frame takes in the total window row height.

Another nice option for newer browsers that support DHTML would be the ability to collaspe the left side frames. This would allow the full window to be used for thread and message display (Since these two frames are the ones used 99% of the time). Another option to consider may be to move the left two frames to a drop down menu format at the top of the window. I don't mean using HTML Select here, I mean a nice DHTML javascript driven menu.

The bad thing about all of this is you can never please everone. The more customization by the user the better.