Every single user that we have moved to Widows 7 has had one complaint. Communicator alerts are not being seen. Most do not have audio and unless you are constantly paying attention, it just does not grab you attention like it did in Vista or XP.
"The answer is display settings in Windows 7"
If you zoom your display settings (Control Panel - All Control Panel Items - Display) to Medium (125%) or Larger (150%) You do not get incoming IM notifications or phone notifications with the exception of the flashing status icon in your task-bar. Once we set this back to Smaller - 100% (default) the issue will be fixed