Just a prettier UI is all I've found. I like CS3 better too.

http://www.adobe.com
It shows all the difference

I AGREE .

Whenever there is an upgrade it means they're making things better (but not everytime this happens). Yes, if you are using CS3 and upgraded to CS4 then it takes time to adopt to their new changes in CS4 version but I have seen many people claiming that CS4 is more useful than CS3 because it has more cool features which you can check their official website for the news.

If you continue using CS4 for a few days then you'll know how much you start loving it.

Good luck

Dreamweaver CS3 for Windows brought in the idea of different program layouts depending upon what type of Web designer or developer you were. Dreamweaver CS4 takes that to a new level. There are 8 default layouts including: App Developer, App Developer Plus, Classic, Coder, Coder Plus, Designer, Designer Compact, and Dual Screen. And if that's not enough, you can now define your own, or simply modify an existing one to match exactly what you need it to do. And it no longer matters if you're on a Mac or not - these features are in both Windows and Macintosh versions of Dreamweaver CS4.

Live View of Your Pages:
If you've ever tried to edit a dynamic or data-driven site in Dreamweaver, you know how frustrating that can be. Just hitting the preview button forces you to publish to your "testing server", which for many of us is our live site. But now, Dreamweaver CS4 can preview pages in "live mode" with interactivity and dynamic elements included. It can even load data sources so you can see how those will impact the page. Plus, you can move through JavaScript scripts and stop the script just where you need to work on a design element, giving you much more control over over the design and interactivity as a whole.
Improved CSS Support:
There is a CSS properties navigator as well as the HTML properties that we're used to. These give you greater control over the style properties including creating style rules for exactly the site section you're in. You can then dial back the specificity to however specific or general you need for your CSS document. You can evaluate what CSS styles are impacting areas of your pages. You simply highlight the area that you're not sure of, and alt- or option-click and Dreamweaver CS4 tells you which styles are affecting it. Then you can edit them by clicking on them and they'll open in another window in Dreamweaver.
Photoshop Smart Objects:
With Dreamweaver CS3 you could import images directly from Photoshop, but in CS4, they take that a step further. Now when you drag a Photoshop (PSD) image into Dreamweaver, it creates a "smart object". This generates an optimized Web image ready for you to use in your pages. If you resize the image in Dreamweaver, you can then get an optimized copy of the image at that size. Plus, if you make changes to the original image, they can be reflected into the Web document.
HTML Data Sets and Suggestions for Use:
In Dreamweaver CS3, you could load XML and database data sets into your documents, but once you had them loaded, you had to figure out what to do with them. Dreamweaver CS4 provides some of the more common uses as well as the ability to load HTML pages (with repeating elements) as your data sets.
Subversion Integration:
Dreamweaver CS4 has basic check-in and check-out functionality, like previous versions. But now it integrates with the third-party application Subversion to provide powerful version control and rollback functionality for your Dreamweaver websites.
Author Adobe AIR Applications:
Dreamweaver CS4 now comes with an extension to allow you to author Adobe AIR applications from right within Dreamweaver.
Deprecated Features:
The following features are no longer in Dreamweaver CS4:

* Timelines
* Web services
* Layout mode
* Site Map view
* Java Bean support
* Flash elements (Image Viewer)
* Flash text and Flash buttons
* ASP.NET and JSP server behaviors and recordsets

They are both the same and can do you very nice websites, but if you want to do web designs using simple techniques that are easy and hassle free SiteGrinder can do that for you.