I have been using it for about an hour on my x64 desktop. I was using Ubuntu 12.04 beforehand. The 12.04 is still on one of my disk partitions.
Canonical is apparently going more in the way of pre-installed crapware. There was an Amazon icon on my Launcher, which I removed. People have also been warning the Ubuntu Dash sends your searches to Amazon, I went to System Settings -> Privacy and removed that.
Haven't noticed that much. It may be a little faster, although my Ubuntu desktop usually runs faster when I reboot it, so I can't tell if it will stay this way yet. Doing horizontal resizing of windows seems a little more difficult, some setting must have changed. Firefox's plugin service seems hosed right now, maybe due to all the new Ubuntu installs. The Firefox edit window is acting a little odd as well. It has crapped out a few times in terms of display.
There were no workspaces until I turned them on in settings, they seem down on workspaces - something I had without a problem since fvwm back in the mid-1990s. Hopefully there will still be workspaces in the next Ubuntu version.
It seems like they've added a little more customization ability for the launcher, sizing the launcher, hiding the launcher etc. Or at least made it more obvious. It doesn't work that well but at least it's there.
I noticed they changed other things...grub now just says Ubuntu on top, and has simplified options under that. I guess I'll bump into more things as I go on.