I have one of these watches, I received it as a Christmas gift.
There is very little that the watch can do standalone. Indeed, I had to hack my Galaxy Note 8 to "activate" the watch to enable USB debugging. After that, I installed null_ firmware, which runs a mini version of Android on the watch. It functions just as the Gear normally would, but there is a subsystem where you can access the Android home screen and run/install APK's and other stuff. I have it paired with my iPhone 5 and can tether through that, and answer phone calls. Caller ID does not show up, nor do any notifications, but if you wish, you can run Facebook and other apps. Battery life is reduced some.
All in all, if it wasn't a gift, I couldn't see myself paying $300 for the watch just for the crippled functionality.. but I would pay $150. It's a nice enough piece of tech that it's fun to screw around with and push the limits. I had Torque running on it, paired with my OBDII bluetooth adapter, and I had my car's sensor readouts on my wrist, in real-time. Pretty cool stuff. It's a nice little gadget.
Plus, Samsung has said that they intend on making the Gear work with iPhone at some point. It's really not that strange, you can get XBox apps on iPhone, and you run iTunes on your PC. If there's a demand (which, at the current price, I can't see too much, especially if Apple is working on the iWatch... which I will dump the Samsung for in a second) I can't imagine Samsung would want to box their product into a specific market.
Edit: here is where I researched and gleaned most of my hacking info -
http://forum.xda-developers.com/smartwatch/samsung-galaxy-gear