I think it's the best Gmail notifier program, but unfortunately I could not use it on windows 7.
GmailAssistant 2.0 (2008-09-07)
The problem is that after the first notification (from the tray iconized app) causes the windows task switcher always to be closed immediately after activated (closed right after show) this way the alt+tab is unusable. Also the preview windows of the taskbar elements are closed automatically and immediately. :/
I think the problem comes from something like the focus not released by the notification window.
Hope you will/can fix this as soon as possible, because now I must disable GmailAssistant.
Thanks for the anyway great program!