Unity runs on top of gnome 3. Most of your programs should be fine as long
as they are compatible with the new gnome. Widgets and such will not
likely continue working, as well as all of old gnome panel applets.

From the bottom up, 10.04 LTS looks like kernel > gnome 2 > gnome panel
while 12.04 is kernel > gnome 3 > Compiz > Unity. That is sort of a
gross over-simplification, but the general idea.