Functionalities are countless
You can do lots of things since there are lots of apps avalaible.
Of course, you can see notifications from twitter and Facebook, you can like/favorite, share/retweet and watch the live. You can't write tweets, comments, upgrade your status. With the official app, you can see your text messages, answer with predefined messages or smileys. With a special app like SMS writer (if I recall correctly) you are able to write text messages (ABC AÀÁ 123 keyboard) and send it to any contact you have... and for telephone, well, you are just able to dial a number and that's it (but I've read "call handling" app enables you to activate the speaker and some other functions)
You can control your music with both official and 3rd party apps but that remains simple commands : volume up and down, play pause, skip, next, you won't browse from an album to another one.
I've never heard anything about xda and cnet apps but if you just wanna keep on eye on the news, there's a an app that collects your RSS feeds, basic, simple.
I've only had lags in SMS writer app, but anyway, you can reboot the device simply by pushing the power button for 10 seconds and it will reconnect automatically to your phone via Bluetooth. That being said, sometimes, Bluetooth connection is slow and you can't open apps that have to be connected to your phone (some apps really need connection otherwise it just won't open).
Also, keep in mind that you are not buying a real "Smartwatch". Personally, I think a Smartwatch shouldn't need Bluetooth connection to your phone. Actually, you are buying a watch with some special features, a watch "+++" if you see what I mean. And at that cost, 130$ for a watch that can do more than any other watches, it's a bargain...
I do have my Smartwatch 2 on my wrist, if you need any further information, I'm here!