colinux or
xenlinux are the same as fast as the host system, because the guest systems doesn't have hardware emulated whatsoever.
And in the case of xenlinux, the multiple system you executes runs on the same ring level, however if you want to run windows+linux at the same time without patching windows, you'll need to wait for CPUs with "paravirtualization" registers which should be out (Intel and AMD) this year.
VMware is just too slow for me.
Dual boot is another option, but it's not the same as doing "ALT-TAB" and having another system.
I suppose the paradise of the
cross-platform developer-tester is to have a
Mac x86 with a
CPU w/paravirtualization and 2GB of RAM, and then you install
XENlinux as the OS on
ring 0, and
Windows,
Linux,
FreeBSD and
MacOS X at the same level
ring 1.
ALT-TAB and you're in windows, ALT-TAB and you're in mac os, ...
Windows hangs... no problem, ALT-TAB linux, and so on...