I'd like to see a few things from notifications:
* Keep them skinny and in the top right. This way they never cover more than the toolbar and by-definition only cover the least used items in the toolbar.
* Make them easily and obviously dismissable. Sometimes I want to get right under a notification right when it pops up. So it should be really easy to dismiss.
* Always use 48px icons. Notify-OSD uses god-knows-what size icons and they are ALWAYS blurry which is really annoying. 48px is still small enough to fit in the toolbar-sized form factor and is an extremely common size for app icons to be provided in. It's also large enough to make sure that the icon is easily recognizeable.