Just a quick note to let people know that I've managed to get zimbra up and running on lxc.
Host is an older poweredge 6600, 4xdual core xeon 2.6 with 12 gb ram running ubuntu 10.04 x86.
Container is ubuntu 8.04 x86 6.0.7_GA_2473.UBUNTU8 UBUNTU8 FOSS.
No real issues except for jvm which needed to have it's percentage decreased. More optimizing can be done, but I haven't needed to yet.
Just another option if anyone is looking for and open source vm solution.