I still think the inline spell check is worth the price of admission, but there is a flaw I have found in the new Firefox 2.0. The close tab icon is now on the tab itself, and it is very easy when changing tabs to hit this icon and actually close the tab by mistake. This needs to be fixed.
Update: OK, not a flaw, just a configuration setting to be changed. See comments. I really love Firefox.
Update #2: I had horrible loading times in Google reader with the new Firefox. I am pretty sure it is the browser pre-fetch function, which attempts to pre-load pages linked by the page you are calling up, in case you click on the links. I recommend you turn it to false. Once I did so, Reader popped right up. By the way, I am very much happier with the tweaked version of the new Google reader -- they fixed many of my concerns.