So far, I would agree with most of your assesment.
I haven't tried the collaboration tools as of yet as well. I am waiting to get a machine at work I can load it on to try it out in a Windows 2003 AD envrionment.
I know Microsoft has tried to remove a lot of the flakyness from the explorer shell that I know everyone has had to experience at one time or another. Be it taking for ever to authenticate with a machine on the network in a non AD environment or being god awful over a WAN connection. In my experience, they have gone a long ways with that. It would takes a good 15 seconds for my XP box to authenticate to my 2003 server. Now, Vista will authenticate in a few seconds. I still have to test it in a WAN environment.
The shell seems more responsive in general, even with the AERO glass turned on. I don't find myself staring at that stupid flashlight for seemingly no reason.
I have never really browsed the network graphically. I always know where I want to go anyway. As far as being able to browse the network, can you tell who is the master browser?
The biggest thing in my mind right now, as you mentioned, is the security and the dialogs asking for permission. It's a step in the right direction. Also, if you noticed in Beta 2, you can no longer ignore the dialog. You can't continue unless you click on something. From what I have read, they changed that because Microsoft's security team was able to come up with a cursor spoof attack to trick the user into clicking the "continue" button. So now it functions more like the Control-Alt-Delete log in procedure, apparently utilizing a trusted path to the OS so you can be sure you are talking to the OS and nothing else.
As far as the amount of dialogs, they come up now when I expect them to. Installing software, changing system settings, etc etc. It is definitely better in Beta 2 than it was in the February CTP. It was coming up for relativley minor things.
I'm afraid that if it comes up too much, Joe user is just going to click Continue and not read the dialog. Thus defeating the whole thing. If they were a standard user, though, I believe they would have to enter the admin password kind of like in *nix. I haven't tried this though.
As far as Office is concerned, you are right in that it's going to take some getting used to, but I think it will be OK in the long run. I always kind of despised having to go through menu after menu looking for what I want. Toolbars addressed it in a kinda sorta way.
One thing you should check out, AR, if you haven't already is the Windows Powershell. It's actually a good shell! One big difference between it and shells like bash are it isn't text based. It's object based. Instead of commands returning streams of text, they return objects that you can then manipulate.
Powershell is in RC1 right now:
Here's a link