Mozilla is obviously encouraging people to upgrade to Firefox 3. Some people have delayed in updating due to concerns they have with FF3, such as the new behavior of the address bar and stability concerns. While most of the complaints that people had about FF3 have been addressed since launch, and many other complaints can be overcome by configuration tweaks, it has not swayed every heart.
Even if you are attached to Firefox 2, a lack of future security updates is an important consideration. So, update today!