As part of the Adobe CS3 web basic and premium packages, Dreamweaver could be considered the glue of the web development suite. It is a wysiwyg html editor, but that is probably a significant understatement. A few years ago, when the web was made up of static web pages, this was the must-have program for web development. Now that dynamic web pages and content management systems are the in things, a lot of the luster of dreamweaver has vanished. I still use dreamweaver for the development of BlazingGames, and until I move to a content management system for running my site I will continue using it.
The feature I found most useful was the browser compatibility checking. Quite simply, you run the compatibility check and a list of potential problems appears. This tells you what browsers may have problems with your page and suggests how you can fix the problem. The best part is that this is suppose to be updated regularly so it should be useful even as new problems surface and browsers are updated.
The big feature of the new version is support of ajax in the form of the spry framework. This is actually a really nice addition as it makes it very easy for someone, even those without programming skills, to make a more dynamic web site. Of course, if like me you have no interest in adding ajax to your site because Flash is a thousand times better, there is little reason to upgrade to this new release unless there are other packages in your suite that you regularly use.