I'm trying out Ubuntu 12.04 in Virtualbox at the moment. I couldn't get it past the install stage using Virtualbox 4.1.2 (which comes with Ubuntu 11.10). But downloading Virtualbox 4.1.8 resolved whatever the issue was. So this is just a public service announcement, as I'll bet trying virtualized Ubuntu n+1 in Ubuntu n is a common use case.
I'm also trying it booting from a USB drive. The Ubuntu Live USB Creator tool worked perfectly. It's just rather slow on my bog-standard class-6-SD-card-via-the-generic-card-reader-that-it-came-with. I briefly considered getting a fancy USB3 /eSATA hybrid stick, but then realised that this laptop has a spare drive bay once you take out the never-used optical drive - and a 128GiB Crucial m4 SSD is only trivially more expensive than its equivalent capacity USB stick - and an order of magnitude faster.
Just some data points.