I tried it and its really good. Though there is no noticeable difference apart from look and feel, the Firefox site boasts a lot of things.
I think one of the coolest features that are added to this edition is spell check on text input boxes. I am not sure if there is any other browser that provides this feature, at least none of the browsers that I use provides this feature.
There is another feature called "Caret Browsing" in Firefox (I think its around there for sometime). Its really useful when you wish to move around or copy and paste from a web site that offers more textual content. You have to press F7 when you are in a web page to enable caret browsing. You can use your mouse to move here and there and select contents. It will really be helpful for Unix people who are more used to using key boards to move around.
I would suggest you to refer to the key board short cuts page in the help section of Firefox browser. There are better ways to move around across tabs, selecting tabs randomly, etc.
One of the controversies that I think Firefox might run into might be the integration of anti-phishing features with Firefox and enabling them by default. Its not very trivial to appreciate. As per Firefox documentation, Firefox periodically collects information from net (from what source?) and verifies the sites that you visit against the list that it has. In case if the site you visit is present in the list of phishing sites, you would be prevented from visiting that site.
Okay. Enough of product advertising. A trivia about this release of Firefox. There is a news on the net that Internet Explorer team from Microsoft has sent a cake congratulating the shipping of Firefox 2. I am not sure how authentic this information is though!