Agree. Notifications/Alerts are a very nice feature. I really likes those "counters". They are tiny, but also dominant. I highly recommend to have a similar feature in CB. Little thing with a big impact, IMHO.
BTW, one of my favorite extensions "Cobalt CCK" by mintjoomla has also a build-in notification center and displays those little numbers in list- and details view. The previous J1.5 CCK version had a multiple email alerts for each event, now there is only a common email and summary PLUS this online notification system. Which is a huge difference in UX. Not to mention the reduction of sent emails.
(I also managed to show the number in the respective J! main menu-item title, which can be achieved through a simple override)
@Roland
Thanks for pointing to the JS blog article. Good read.