Ubuntu Guide posted a quick tip about fixing the no background wallpaper problem after upgrading to Ubuntu 11.04 Natty
Ubuntu 11.04 has come out for few days, if you choose to upgrade from a previous Ubuntu edition you may encounter no wallpaper displaying problem in Unity. Theres only a white background and wallpaper chosen in Appearance window wont display any more.no background wallpaper problem after upgrading to Ubuntu 11.04 Natty