Ubuntu 11.10 is based on GNOME 3/GTK+3, meaning numerous applications have been ported to GNOME 3.
Ubuntu Software Center makes no exception and, in the last weeks, we have seen an accelerated process towards this goal with a two-sided approach (the default Ubuntu Software Center was the "old" GTK+2 version, but the GTK+3 version was available only by typing "software-center-gtk3" into a terminal).
Ubuntu Software Center 4.1.19 (just now updated to 4.1.20) comes with the GTK+3 UI by default, exposing quite a polished, modern, fancy interface.