A nice client. Two issues though: 1) it seems to have some synchronicity problems from time to time (not enough asynchronous processing, or is my machine just too slow?), 2) it looks like it's designed for full screen but I want my twitter stream to be in an Avalon-like side-panel. Aero-Snap'ing it to the side of the screen will not do the trick because that still uses up half the screen real-estate and it wohn't gracefully reconfigure itself to a snapped configuration (slim, one column). Actually the best integration is probably like "hot air" where the news start at the bottom right side of the screen and then float upwards whilst becomming increasingly transparent (they only float upwards if new tweets arrive before they've disappeared entirely).
Anyway, that's just my point of view. It's clear that you've made a nice client that looks just as nice as, if not nicer than, other twitter clients.
Actually, it looks as if you'll have taken care of my main concern if you just hide the client from the taskbar when minimized.