Linux-VServer takes a different approach to running virual servers than most arrangements - a kernel patch to the host system gives it the concept of "contexts" which is the heart of Linux-VServer.

Essentially, every virtual vserver shares the same kernel as the host system, although they are all full isolated and protected form each other. This means it's no use for testing new kernels (which is on of the main aims of User-Mode linux), but is more efficient for production servers that most of us run.

It makes sense that it's more efficient than User-Mode Linux, and I would guess that it should be faster than VMware as well. (Incidentally I love VMware, and use it on production servers).

Thanks to Guan for the link.