KVM is the "preferred" Linux virtualisation solution (at least as long as you have hardware support that is). Beware that the management tools for KVM are still fairly immature - VMware's vSphere product for example is still leagues ahead in terms of production usage.

Feature wise however, KVM is pretty good even if the libvirt abstraction layer support tends to lag a little behind.

The KVM packages for Debian are a little old in this fast changing game - one bug we've seen in particular is that qcow images can be corrupted. KVM is being merged back into qemu and this is what we are swapping over to. Using Michael Tokarev's packages as a starting point, we've created some Qemu-KVM 0.11.0-rc2 packages for people to enjoy. These packages are for Debian Lenny (v5.0) 32-bit only at the moment and you will need the libxenstore3.0 packages from unstable in order to fix a nasty link issue.

All part of our commitment to work with the community and give back to it, we've sent some fixes along to Michael and are also making these packages available for download. We have a new libvirt (with additional fixes) available as well which you will probably need.

One interesting issue we saw occurred when KVM was using an old Qemu BIOS - we then saw this on startup:

Kernel panic - not syncing: IO-APIC + timer doesn't work!
Boot with apic=debug and send a report.
Then try booting with the 'noapic' option.

Without further ado, either see our packages page or use this apt-get line:

deb http://bitcube.co.uk/repo/ lenny main contrib non-free