Firefox (1.5 and 2.x) appears to the best as most if not all the GUIs work with it. The user portal provides extra info that isn't in IE7 when trying to release e-mail.
IE6 haven't tried yet.
IE 7, dashboard and menus work sometimes, but can give the impression the ASG is overloaded, where as it is only IE that needs a restart. The user portal sort of works in IE 7, but when you try to release e-mail nothing happens.
Konqueror, don't even try.
Ian M