Michel,
I'm at the office now, using the monitor at 1280x1024 and the top left frame font is very tiny indeed. The message frame font could definately also stand an increase by a point or two also.
It would be nice if you could cookie base the CSS fontsize selection. On my notebook at 1024x768 the fonts are ok, but the office machine they are too small. If it were cookie based those of us using multiple machines wouldn't have to keep reconfiguring.
It would also be nice if the message editbox width were configurable like it is over on the Wiki.