Am I the only one who finds the GUI so slow? You click, nothing happens, you drag, the element doesn't follow, the hand-cursor shows up over elements that aren't clickable, you can't resize the left menu even if there's a resize handler...
I'm using IE 7 on WinXP. I tried Opera but Zimbra doesn't even accept Opera
Maybe Zimbra has too much stuff making it full of Javascript and slow? It reminds me RoundCube a little bit, both are slow and non-responsive. I wish they were both as fast as Gmail's interface.