Here's my £0.02, all its weight thrown behind Ubuntu - although on my rig I prefer Matlab Windows based as some crucial toolboxes used to lack Linux support and even if they worked now, don't fix what ain't broke. After saying bye to the venerable but aging Gentoo, we (is I & colleagues) migrated to a variety of systems, the favoured setup proving to be Kubuntu as a virtual machine in Sun VirtualBox, running on top of Vista or Mac. It's actually a very smooth running combo, with full networking and sound and bells and whistles one can only desire, and the switch between the two systems takes as much as a keystroke.
Even if you prefer the separate boot option, I recall that while installing Kubuntu, it offered to install as a standalone system. I'd be interested to see it work, do post your experience if you decide to go for it
