DOF is still a mystery
I'll bite. Here's a decent example of DOF (the best one I have on my work computer.) See how the flower is pretty sharp compared to the background concrete/ door frame? It helps draw focus to the subject (in this case, a hibiscus flower) instead of the background. It could have been better, but I've only been learning about this stuff for about a month.

Excuse the oversaturated-ness, I messed around with this one a lot in Dynamic Photo.
Sleeper3 -- I apologize for bitching about you DOF on that one. I didn't realize is was a crop. You are obviously a pretty accomplished photographer judging by your other pics.
(hi)