Well you can't set the option - we can in the AdminCP though. I prefer the automatic lightbox initiation on hover. Depending on how the rest of the community feels though, I'd be glad to change it.
Uhh, sometimes when I hover by mistake it makes my browser go slower... I already have a crappy connection as it is..
Not necessarily a fan of "On Hover" myself. When I am reading something, I'll just nudge my mouse to get it out of the way. If it happens to land over an attachment the lightbox is really annoying and counterproductive.