There's a new version of the OS X system notification tool Growl, and it's kind of amazing.
You can "close" notifications now, and it manages the problem of too many notifications staking up, if the system somehow runs out of room. (Say you walk away from the network or your computer for a while. Additionally, there are now more notification themes, which is very welcome.
We just need to port this to mobile devices like the iPhone and iPod touch, and so forth. The program also has the capiability to mange sending/reciving notifications from other computers, which I think would be really great for an iphone/etc.
I mean you could kludge something together with email notifications, but that kind of solution is never the same...