It's interesting - I use a lot of features of OS X that I think most people don't touch often (I'm probably one of the only people on HN who frequently launches apps from Launchpad with the four-finger squeeze, for instance) - but notifications bar and mission control are two that I've never found any use for. (I'm an Cmd+Tabber)

Indeed, Notifications has an annoying habit of locking up an otherewise solid 10.8.5 so I can't command+tab between apps. It always returns after 45-90 seconds, and I can kill it by bringing up spotlight and launching activity monitor - but that's the only impact that the notification tray has made on me. (Though, notifications themselves, akin to what Growl used to do, are kind of handy - except for the annoying one telling me I have to update my computer that I can't stop from coming back - particularly harsh when you are doing a presentation on a projector)