My wife and I use it on the dock almost all of the time. I expect when we travel, it will get some independent use, but it's so comfortable to not have to hold it up to view, and convenient to type on real keys instead of glass. Unless we are playing a game that needs physical movement, there doesn't seem to be much incentive to separate it.
There is also the incredible battery life with the dock connected, and no concern that we will run it dry throughout the day, no matter how hard we use it. Regarding heat, it's not an issue. If anything, it gets more heat from my legs than it radiates from within. Maybe my judgement on this is a little skewed, since I'm comparing it to my 7lb + toaster oven HP 9000, but it does stay quite cool.