After battling diagnosed ADHD for about 12 years (save the ADD/ADHD jokes/debates please) I have found that the only way I can learn any complex material is to go to the "workshed" in my back yard.
My workshed is insulated with power/ac/heat, but the 'office' portition is a small 8x10' area. There is 1 window which is about 1x2' and it's about 7 feet off the floor. My shed has no computer, no video games. It is away from everyone else, there could be a house party going on in my house and I would be completely unaware of it. In my where I sit I have notes of useful formulas, theorems, identities, and notes all pinned up on my walls.
Now what does this have to do with concentration span? Well, I'm so glad you asked. Anytime that I sit anywhere else my concentration span is
extremely short and I lose wind very quickly. However I have found that if I am in the proper environment, I go so long and get so involved with what I'm doing that I will "forget" to eat, like Evo previously mentioned. So for me and my racing "adhd" mind, it's all dependent on the environment that I place myself in, and eliminating my distractions.
in fact, here's a ballin glamor shot
http://photos-a.ak.facebook.com/photos-ak-sf2p/v298/92/1/212601942/n212601942_30765816_2658.jpg
Occassionaly when I am teaching myself math (currently calc2) I'll bring my notebook so that I can get on #math on irc.efnet.net for assistance.
granted it may not be as exciting as this
But like Big Daddy Kane, I get the Job Done