Forum OpenACS Q&A: Re: Gush: vservers as development/production environment
If each user needs his own different Linux kernel (e.g., for kernel testing), you need UML. If not, use Vservers instead. UML will incur a much larger performance hit.
As Xen demonstrates, it's entirely possibly to run a fully virtualized Linux (or Windows for that matter), kernel and all, with very little performance loss vs. running on the bare metal. But that's really not what UML is intended for.
I'll do the google thing shortly. I was just asking around to see if anyone had any personal experience or pointers. From what I've read and heard so far, vserver seems better suited for my purposes.