Another point I made: you can play with DOF calculators all day but nothing replaces actual experience. Pushing the boundaries is fun and educational. A picture is worth ... well, more than a number in a DOF calculator.
I think the line about experience ties in with how I think about lenses on a crop camera. I shoot with a 7D now and have been using a crop body for all of my digital "life" (starting with a D60). Before that, I shot film.
When I select a lens now, I never think in terms of "what is the crop equivalent of the FF lens that I want to use?" I select a lens based on my experience with lenses on a crop camera. I know what I'll get at 200mm or 300mm. I know the effects I'll see for f/2.8 or f/4, or f/8 or anything else for that matter.
Unless you are switching back and forth between ff and crop bodies and really find you need to think in terms of what you see with one on the other, I think it's mostly a non-issue. I know what a 70-200/2.8 is going to give me on my 7D.
This weekend, I shot with a 5DIII. This is the first time I've used a ff body since I put down my Elan II E for the D60. I never used the 70-200/2.8 with the Elan II E but it wasn't confusing at all. I didn't have to think about what it would show relative to the 7D. But, I did know that in familiar situations it would help to add a 1.4x teleconverter to get the reach.
Once you are actually shooting, the whole idea of equivalence and crop vs. ff lenses becomes a lot less important. A lens is a lens and a little experience makes everything pretty simple.