My response to one of our sales folks when asked to quote hours on upgrading three existing XP boxes to Windows 7:
If we are re-installing and can do them all at once, about 4 hours, otherwise probably 2 hours each. In-Place upgrade (which may not be available and should be avoided anyhow) about 12 hours (this includes being forced to start over and install from scratch when the in-place upgrade goes to hell).
Seriously, folks. We’ve been warning you about this for over a year now.