Installed the first GM about a little over a week ago; it had already been out for 2 weeks or so. GM #2 was released a few days ago
If you've going from Snow Leopard to Mavericks, tons of new features. Going from ML to Mavericks, uummmm, not many noticeable features, at least for me... yet. The quick change I noticed was, you have to hold the power button about 2 seconds to bring the power buttons. Previously, a single button press would bring those buttons up. Right now, a single button press puts the display to sleep.
And the thing I like about the OS = it's freeeeeeeeeeee
edit:
I'll be doing a fresh install of the OS in a few minutes. Can't be running the first GM, y0