There will always be people who will argue "I want the Finder to work *my* way by doing ____ or looking ____, and oh yeah, I hate that new widget". Unfortunately, the usability stuff will probably never be completely agreed upon. Usability issues aside, here is what I've noticed in terms of performance-type improvements/changes:
The Finder is much more responsive. There is much less spinning beach ball, and directories load much faster.
I think there is a lot of confusion about threading and the spinning beach ball, since everytime somebody sees one they seem to think "needs more threading" (based on what I've read within other threads in these forums). When you thread something and thus de-prioritize it, while stuff in the foreground is more responsive, the task that has been threaded will take longer to complete as it takes some time to spawn the thread initially, and a longer time to complete a given task given its lower priority. When I double click on a directory, I want the quickest response possible - I want it to be a foreground task.
Perhaps my technical information is not 100% accurate, but my point is that threading doesn't magically make everything better and faster. There are tradeoffs and decisions which have to be made, as well as compromises. I think some great decisions have been made within the Finder. I'm happy with its performance, although I'm sure some have been expecting absolute perfection and will be somewhat disappointed.
When remote shares have been disconneccted for whatever reason, the Finder will no longer hang. Now, after a while, a dialog appears asking if you want to reconnect to the server. If you dismiss this, you can go back to your work. If the share cannot be reconnected to, a dialog appears saying that the share has been expectingly disconnected. My description of the context in which these events take place may not be completely correct, but my point is that there are procedures in place now to treat this issue.
I know there is another thread about the Finder within previous Panther builds, but I thought that perhaps we could start one about the GM.