At Crossett Brook Middle School in Waterbury/Duxbury, Vermont, we have about 260 student computers, all but 6 (legacy XP for DragonDictate) using UberMix. We have added a lot of programs, including the Lock-Down Browser for the upcoming Smarter Balanced Assessment. (I don't think that many of the programs other than Firefox and Chrome have had much use yet).
There are:
50 Asus netbooks
25 HP netbooks
65 HP notebooks (6465b, 6735b, nx6125)
120 HP desktops (5100, 5850)
Students have been using Ubuntu for a couple of years. This is the first year in which we are using UberMix and have been doing so for only a month. However, it seems to be going fine.
We also use Ubuntu 12.04 on all content teacher notebooks, but are presently using gnome desktop 2, not UberMix.