[bscphil]

Anecdata: back in the days when I was using Ubuntu (pre-Unity) on what was even at the time moderately old hardware, there was an obvious difference. Standard bootup took 20-30 seconds, resuming from hibernation took multiple minutes.

Just thinking about it on an abstract level, it's not that unintuitive that resuming from hibernation should be slower than both cold boot and resuming from sleep. When you cold boot you need to load the kernel and startup programs into memory. With hibernation you need to load the whole previous operating state into storage, which is going to mean multiple GBs need to be read from your swap partition into memory. It's not hard to imagine that on many systems the hard drive will be the slowest piece of hardware.