CS4 follows the same distribution model as CS3 with 6 different editions of the software available. The editions are all the same as CS3 - Design Standard and Premium, Web Standard and Premium, a Production Premium and the Master Collection. Each edition differs only in which Adobe products are included, and the Master Collection contains everything.

CS4 comes with a smattering of new features, including increased integration with Flex 4 through Flash and Firework's ability to export FXG graphics. CS4 seems to be focused a lot on integration and collaboration, and shows off a new standardized Adobe UI. If you were sick of the transparent-background and floating panels in previous generations of Adobe products, you'll be happy to hear that the new UI gets rid of all of that.

Every product seems to have received some significant upgrades. As an RIA developer, I'm most excited about the aforementioned Flex integration. Another notable change seems to be the role that Adobe Device Central plays in CS4. Though Device Central was included in Creative Suite 3, it seems to be getting a lot more attention in CS4 as Adobe targets the mobile market. It provides improved support for video and some new testing tools.

Adobe has more info on the CS4 homepage - check it out for a full list of feature updates by product along with a comparison chart showing the differences between the versions.

To cap things off, here's a video by "DesignMinstrel" Mike Chambers twittered last night about the new features in CS4:

If that doesn't get you excited, I don't know what will.