I have the wifi version of the 10.1, and I must say this is an incredible device. Those who are getting yours for the first time will realize that Samsung did it right with this tablet.
I use the hotspot feature on my Evo 4g to connect to the internet whenever wifi is not available. However, I will say that I like the idea of a seperate data plan for the tablets.
Using the hotspot feature does require you to never be far from a charger. Otherwise, in my experience anyway, a dead phone battery will be the result.
I really wish that Samsung could have worked out a deal with the carriers to provide data on demand the way it's done on the iPad. No worry about contracts. Just activate, pay, use, and deactivate your data right on the tablet. This way you only use what you pay for. In my opinion, this is the way all data should be handled on tablets.