If you like the Cosmos background slideshow in Ubuntu 10.04, there is a way to create your own. It is called Create Background Slideshow (CreBS). It is not in the Ubuntu repositories, but I think they should add it. You have to install it from a PPA.
It is actually pretty simple, just type the following in the terminal:
sudo add-apt-repository ppa:crebs/ppa
Then you need to update your software list, just type the following in the terminal:
sudo apt-get update
And finally install crebs, just type the following in the terminal:
sudo apt-get install crebs
To run the program go to System > Preferences > Create Background Slideshow.
Use the plus sign to add wallpaper to the slideshow. I suggested putting the ones you want to use in a special folder. I also suggest you use pictures that are the correct dimensions for your desktop.
You can control how often they switch and how fast they transition. You can customize length and style as well. Don’t forget to give it a name.
Once this is done, you just right click on your desktop and select Change Desktop Background. Select the slideshow you created. And that’s it. Enjoy.
For more information about crebs go to: