[Brian]

Rereading my post, I think I was a bit too brief. My calendar tells me where I need to be at what times; OmniFocus holds a big stack of stuff I can do in between those commitments.

Within OmniFocus, I try to build in flexibility by dividing my stuff up into "I gotta do this" and "I wanna do this" lists. Former items get due times for today, latter items just get flagged, and I try not to cram unrealistic quantities of stuff onto the "gotta do" list.