I don't boot to a desktop- I boot to a login screen, plus mine wastes 10 seconds asking which OS to boot :) That's for my main.
Every other box I just hibernate, which powers down as much as possible (only laptops truly power off) writing an image to disk. The laptop sleeps if plugged in.
I will time them next time I power down.
Then there is my server-
linpear:/etc# uptime
14:22:52 up 146 days, 21:56, 1 user, load average: 0.08, 0.04, 0.05
146 days since reboot, which was for a switch to 8 cores and a doubling of disk space :)