Login Slow After Long Idle Time

I've noticed when I log in to my computer at work first thing in the morning, it's very slow the first time. The machine does not go to sleep, spin down hard disks nor shutdown, so it's not an Energy Saver issue. After the first, slow login, subsequent logins are normal and speedy. But what's weirdest of all is that this does not occur on my home system, which is actually a slightly slower machine. I figure it's probably got something to do with my home account settings, or network settings, but I'll be damned if I can figure out the difference. And still, why would login times change after a long idle period. It just doesn't make sense. All I can think is maybe it's stale cache being flushed. Either way, it's a little weird and a slightly annoying way to start the day.

Theories? Anyone?