Edit: 9-15-11, looks like Ubuntu's latest update has fixed this!!
One thing that frustrates me about Ubuntu 11.04 and Unity is when I am in Mendeley Desktop and want to combine authors or do something on the LHS the sidebar will pop up and remain there blocking part of the window. At first I thought it was broken, but it is, not really buggy, just flawed. The way I figured how to get it to hide again is go to somewhere like an internet page and click and drag across some text to highlight, then click in the highlighted text and drag away like you're going to place it somewhere else where you'll see the hand in a fist, the transparent text, and a plus sign, and the side bar will hide again once you release the button.
Also see here where I posted on AskUbuntu - http://askubuntu.com/:
What to do when Unity's Launcher gets stuck open? - http://askubuntu.com/questions/41962/what-to-do-when-unitys-launcher-gets-stuck-open/44165#44165