I would fall into the second catagory - always on email doesn't matter.
Work stuff I try to take care of during work hours.
Home Stuff I *try* to take care of whenever
I generally delete the hundreds of server messages I get a day on my BB immediately unless its the rare instance I have to act on one of them, and constantly sort them into appropriate folders in my .ost for future reference.
Online stuff (forums, this etc.) I generally take care of whenever there is a computer on.
Lately I've tried really really really hard to not turn on my computer at home at night. It rarely happens, but at least I refuse to start trillian on this one unless its a day I'm working from home, and try to only download email on the weekends (I use webmail for personal mail during the week and POP it to a .pst for mostly archival reasons at home), or at least wait until Thursday night like now (I generally work from home on Fridays).