I use Ubuntu at work, and I did the jump to 11.04. Have to say it's different, and there is some getting used to to do. However, I've seen some irritating differences with the Unity desktop (not present with the Ubuntu Classic/Gnome one).
First, it's difficult to move a windows between screens (not workspaces), some will move, others will not (without any logic in between, as it may be the same window that didn't want to move initially).
Second, it's impossible to keep the web browser I had. I usually use Google Chrome as a browser (as it is faster and more stable than Firefox). However, with this new version, even when Chrome is set as my default browser, Firefox opens for links sent via instant messaging or email, which is definitely counter-productive.
Also, some applications have their menu bars at the top of the screen (à la MacOS X), and others in their window (à la Windows). And even better, some applications are not correctly positioned on the screen, as when I click on an element of the window, I actually have to click on the element before it.
Finally, the launch bar is a little difficult to getting a hold onto. It sometimes appears on the left of my desktop, others in the middle. At first, I had difficulty making it appear/disappear, but it's slowly coming in.
One thing is for sure. Ubuntu is going to change, and with all the feedback they're going to get with this release, they are going to improve on top of Unity, or scrap it altogether.