Server Virtualisation - Live Migration vs. Quick Migration.

I'd really like to get to the bottom of this.

In the event of a hardware failure, both VMware and Microsoft's Server Virtualisation solutions are equal - the guest machines will be restarted on another physical node.

In the event of some planned downtime, we both have the ability to move the guest machines to another physical node - but we do it at different speeds (less than a second vs. a few seconds).

Here's my question (and I do agree that it's nice to have less than one second - that's why we will have that feature at some time in the future):

If you're planning on moving a running server (guest), do you do it now?  or do you wait until the workload is small (the users have all gone home)?

i.e. Do you NEED less than a second to failover (or will a couple of seconds do)?

Please post your answer (and be honest - the question is "do you NEED less than a second") - I'll count up the replies...

Thanks,

Dave