Every time adobe revs there's a learning curve, this one will be no different. I look at the screenshot and can see where changes in my workflow will need to happen, but nothing drastic. It doesn't seem all that bad to me.
I do dislike some of the Windows-centric interfaces I'm now finding in CS3 (choosing a destination for a freshly saved file comes to mind, horrid), if I had my way I'd rather not see them in my apps. But I'm used to working on the underdog platform, some sacrifices have to be made now and then.
I also feel like I haven't gotten my money out of CS3 yet, now they're revving it already??? I'm an independent, I pay for my own upgrades, I'm not paying for another one so darn soon! I get the feeling I'm skipping CS4, at least I'll be a late, late adopter. Unless CS4 has another ground breaking, time saving tool like Quick Selection Tool it won't be worth my hard earned cash.
And my opinion about Macromedia UI, it SUCKS! Flash has the worst interface I've ever had to work with. It feels like every menu is a hack. But I work mainly with Adobe products (more than a decade now), maybe that's why.