Maybe this belongs solely on Rhythmbox's site but I would like to be able to apply my own album artwork to rather than only having Rhythmbox download it's best guess.
I listen to allot of music that Rhythmbox can't find covers for or that it applies incorrect covers to. It would nice to get consistency but defining my own downloaded art work.

This is my only complaint with Rhythmbox, I otherwise love it's simplicity, functionality and integration with the desktop.

Perhaps there's a way to do this already, but I haven't learned it.

See: http://www.ubuntu.sun.ac.za/wiki/index.php/Pulseaudio

It is very complex and intimidating for a new user to activate pulseaudio if using an old Ubuntu install CD.

Provide a method to upgrade and setup in a simple way.

This is one of the most annoying small things I've seen.
In Totem, when changing the volume, the bar comes up and you can change it, but the only way to get rid of it again is to re-click the Totem player.

If you click anywhere other than the adjust bar, it should close it.
Rhythmbox does this properly, so Totem should too.

It seems funny sometimes to see newbies in the forums asking about software, and a suggestion is made by someone to search for a package in synaptic, only to have the newbie reply back, "I couldn't find it." Then be told they have to enable the restricted packages and try again.

Couldn't they be given a little sideshow with music and narration that explains what repositories are, that appears mid way through install (You know, during the time they're browsing the Internet or playing Sudoku) and ask them, "Do you want to enable restricted repositories."

Along those same lines, ask them, "Do you want to enable flash? Do you agree to these terms or don't you agree?" And so on. I think it would make great use of their time while their waiting for the rest of the system to install, as well as save the forums a lot of trouble with having to deal with some of the most common issues brought up, repeating itself and wasting time.