It looks as though they've taken a leaf from Lightroom as to screen layout. Does anyone who's worked with the beta know whether the right-hand panel can be minimized or toggled on/off? In Lightroom there's that little triangle on the right edge to hide/show the edit panes. Call me old-fashioned but I have a 4:3 aspect ratio display and don't have any particularly desire to switch to something wider.
I've been testing CS4 and it never ocured to me that CS4 was like LR in that respect. Probably as I use a second monitor and with laptop I prefer to have panels displayed or tabbed out of sight altogether. No little triangles.
How the interface works is quite subtle and also changes depending on screen mode and how you place your panels/pallettes against the sides. You can set it up to work how you like.
It's much better than CS3, especially on the Mac as you don't see through to desktop anymore [optional if you want old faffy interface], but the new interface is implemented slightly better on PC, as it is more coherent and uses less vertical real estate.
Therte have been a lot of moans about new interface, from those who haven't used it, but it is
Is it worth upgrading? All a matter of priorities, if new features help your workflow then cough up. Though as many of the improvements are not so in your face, it's not until you use the older version you realise how much better it is. I've not used CS3 for work since June.
Bridge CS4 is worth upgrade money on its own, it's sooooo much better. I've barely used LR of late. Not to mention how good ACR5 is.