My quickest booting Mac is a Color Classic with System 7.0.1
My slowest booting Mac is a Power Mac G5 Quad running Mac OS X 10.5.8
The Color Classic is done while the Quad just starts to show the grey screen with Apple logo.
Same goes for PC's...: Seen a 486 DX100 boot DOS 6.22? Seen a Core i7 boot Windows 7 with virus scanners?
Yea the uptime I had running OS X (not as a server) was well passed a month. Easy. Though, using Disk Utility to help set things strait was required because after 20 or so days it seems the system would page to the disk.