1. See who is calling without taking out your phone, button press will tell your phone you've decided not to answer the call to it stops ringing.
2. See the text of new messages from SMS/email/twitter and likely any other source you care to see. You can scroll up and down to read them.
3. 5-7 days between charges. Some apps or faces will shorten this by a LOT. 99% of the time I use the two functions above, on a 4 day trip out of town now, didn't even bother to bring the charging cable.
4. See how many voicemails, texts, email you have waiting.
5. Control Tasker (Android only) which brings up a bunch of simple things you can do.
6. Current weather
I wouldn't want to try to enter text on it, only has 4 buttons, but if you want to see if it's worth leaving the clean room it's great. You could likely set up a couple stock messages and send them if you really wanted to, not sure if there is an app or if you'd have to get Tasker to do it.