My ADC seed became available today. I've installed it on a MacBook Pro and a PowerMac G5.
First impressions... XCode 3 is more stable than in 9A410.
"3D" Dock - I hate it. First of all... it looks messy and cluttered. The 2D Dock looks a lot more elegant and a lot cleaner. The icons on the "3D" dock have a large gap below them just to show off the reflection... which gets boring after 10 seconds. At the moment, dragging items into the Dock is tricky, especially if the dock is vertical.
The menu bar at the top... rubbish!
It you have a background image which is even remotely complex, then it becomes very difficult to read the text. Even some of Apple's supplied background images have cause problems.
The new Cocoa Finder. Very good UI improvements. Coverflow is okay, but I guess it will be the least used out of the four possible views. The network mapping is really good. SMB shares have a good icon. It's a CRT monitor showing a BSOD. lol
Stacks: not sure about this one. In previous versions of OS X, you can drag a folder down on to the right-hand side of the dock. Left clicking opens a Finder window, and right clicking makes a kind of Start menu.
In Leopard, Stacks is just a prettied up version of what previous releases can already do. Except, to get a Finder window with Stacks, you have to do two clicks. In older versions, you just use one click.
The new Frontrow. I never liked the Apple TV UI, it seems a step backwards from Frontrow in Tiger... and now they've put the same UI into Leopard. There's no nice 3D transition from the desktop to Frontrow in Leopard. Overall.. unimpressed... but hopefully it'll improve by the time the general release is available.
The main things I'm pleased about is that XCode is more stable, so I can now hopefully dump XCode 2.4 an move some code over to ObjC 2.0 and use some of the new APIs like Core Animation in my application.
There's a lot of work that still has to be done before release. Hopefully by then, Apple will include options for a 2D Dock, and an opaque menu bar.