I am typing this from the latest Windows Vista CTP (build 5308) which I downloaded in the middle of the download blitz, therefore taking about 20+ hours. But it was definitely worth the wait. I think with the previous build, I spent more time trying to install it than I did actually playing with it. However I can already tell that I am really liking this build. It's really tight and outside of some small issues which don't bother me in the least (due to the fact that this is a CTP), I feel like I can really now take a good look at this new operating system.
I think getting past the novelty of the Aero/Glass feature is going to be a small challenge for many users. It's just slick and pretty. Once again, I completely forgot how to get the accordion affect of layering open program windows. It took me a lot of time (I'm embarrassed to say how long I actually spent just to see this again) to find out how to get it. One reason is because I seem to be the only person in the world who calls it "accordion" - though spell check just made me realize it is because I was spelling accordion wrong! (I was typing “accordian” - oops! I get a lot more hits when I spell it correctly ;-) ) Googling brought me to one of my own posts! I finally discovered that the effect has been renamed "Flip 3D". It is supposed to be accessible from a keyboard shortcut of Windows Key/Shift, but isn't working for me. No worries though because it could either be a CTP issue or the fact that I am working with a beta video driver from Nvidia which comes with no guarantees. In fact, with experimentation, I found that I can come close to the flip 3D effect with Windows/Tab - but that looks like a little glitch.
This is just a screenshot of Flip 3D I copied from the Vista Features page.

I'll wait and see on this one.
I do think that there are things that will take some getting used to, in the same way that many of us have to set Windows XP Control Panel to "classic view" to access things in a familiar way, there are things I found just in trying to get the computer set up and install drivers that were frustrating because I wanted to do them the way I am used to. This isn't a big problem for me, only a small price to pay for what we will be gaining with this version.
My neice has been fiddling with this computer now all day and quickly found and enjoyed the new default games. I kept looking at the SOlitaire program and wondering if it is the one that Chris Sells said he was writing as his "test app" for Avalon.
I also love the tablet pc features of Vista which have become much more intuitive since XP and fine-tuned since the earlier Vista previews I have seen. In addition to the great visual clues like the water drop for a right click, the handwriting reco is much improved. I'm a great guinea pig as I have really nasty handwriting.
I hadn't installed many apps on the previous build of Vista but I think I will make the investment this time. I will not only try the Office 12 Beta again but I'm going to go for it with VS2005. I know that as soon as the next build of Vista is released, I'll be repaving the machine again, but I'm ready to play with it now and it's not that much effort to reinstall. In fact, I think if I hadn't chosen to reformat the drive as part of the 5308 install, I would have had the install finished in a very short amount of time - much less than a typical Windows XP install.
A technical note. I am using a Toshiba Tecra M4. I downloaded the latest beta drivers from NVidia that were created for this build and released on Feb 23. My video card is a Geforce Go 6600 TE something or other and I am using the GeForce 6600 driver. That is giving me glass (with a few problems that could be my own doing or the beta driver) and my tablet pc functionality with no conflicts. Wheeeeeeee.