I thought everybody used hibernate/sleep... Except,maybe, Linux aficionados. Although... even Linux distros hibernate pretty well these days.
It's not really about hitting/not hitting save, but more about 1- not loosing time reopening every single app and document you were working on (that is, if you have several opened windows, etc.), 2- easily keep track of you were doing before "shutting down" your computer.
(BTW : I rarely hibernate/sleep without saving my work first.)
Like Tom, I might have had a few problems here and there, but overall, Hibernate, sleep etc. have been real saviors (owned three different laptops over the last 9-10 years, each running windows XP -- well... 2000 first). It's so important to me that I would probably consider switching to Apple if hibernate/sleep/standby weren't there... But maybe that's because I also have a lot of stuff in my startup folder and I usually have about 12-20 windows opened, etc. When I shutdown/restart, it takes so loooong before I can actually do something. I hate restarts.