These seem like the best community wallpapers so far and I'm really glad they've finally decided to include some non-photos as wallpapers (we've had enough flowers in 10.10).
The default Ubuntu 11.04 wallpaper has been slightly modified:
I have made subtle changes and introduced new light refractions. We can continue to add light streams and re-balance with each release - the landscape becomes gently lighter and brighter and gains in complexity to reflect our drive towards 12.04 :)
IMHO as we move towards becoming more of a 'household' platform and with the great changes coming with Unity (launcher/dash) general users will get reassurance from the familiarity of the wallpaper and will also identify with it as part of our personality in new screenshots.
Download all the Ubuntu 11.04 community wallpapers from HERE (I didn't link to the .deb because it would replace your current community wallpapers package).