I can't check right now so I don't know offhand if Gnome has the option the cycle between backgrounds every so many minutes, but it's an option I can safely assume many users would expect to see.

I've seen OS X and some other things for Windows do an instant and distracting switch between backgrounds, but what about a simple fade/blend between images? Filter effects could also be used for an interesting shift, like additive (the RGB values of the two images are added together) or subtractive (the RGB value of one image subtracts from another) blending could make for quite an experience when using different backgrounds that cycle.

There should be a way to automatically set the weather applet to the current location you are at, using GPS.

This will make life easier for people who move around alot with their laptops, whilst eliminating the need for any configuration when they travel.