Its pretty stable. I've been running it for a month now and I've had one crash in the time.
I usually have a few copies open as our project is split in several apps.
Its not perfect though, there is one annoying bug. If you code to an interface and get an error in an implementation class, when you compile the errors appear then disappear from the error list (not just interfaces, but thats mainly where I see it).
You have to use the output message to get to them.
We have logged this with Microsoft Connect. They came back saying they could not recreate and asked us to video capture, which we did.
Its happening for all of us in the team so it seems to be an issue in visual studio itself.
Its a bit of a memory hog as well, and the wpf ide can be a little clunky, especially for the lads with the slower machines and no hardware graphics card (which 2010 can use to speed up IDE performance).