I've finally gotten around to installing and using Mozilla Firefox 2.0 and so far so good. It doesn't feel dramatically different from Firefox 1.5 (although I haven't done any stringent comparison testing).
The migration from 1.5 to 2.0 was just installing 2.0. All of my 1.5 configuration settings, passwords, bookmarks, etc. just flowed right into 2.0. Simply install 2.0 and startup the new browser and everything comes along for the ride.
One change that I did notice that perturbed me a bit (although I am sure there are others who will like this) is that the tabs in the tab bar now have a setting for a minimum width and automatically start scrolling when the tab bar is full. To me that takes away a lot of the value of tabs in that I can't immediately see the entire set of tabs I have (and I usually have many).
After looking at the preferences that are configurable through the Options screen (and finding nothing to help me), I was able to find the "about:config" screen which allows you to set what looks like billions of preferences. Setting the browser.tabs.tabMinWidth value to 0 disables tab scrolling. Of course, when the tabs get too small, I won't be able to see them either, but then I will probably notice them getting that small and start a second or third Firefox window (yeah, that sometimes happens).
Even with this little quirk (that was easily fixed), I like Firefox and it's my primary browser for most browser work.