I have suffered from this affliction for quite some time. Someone will be talking to me, and they'll say something really interesting, but then go on to talk about less interesting stuff. Meanwhile, I've stopped paying attention to them, and my mind is humming away, thinking about all the aspects of this one really interesting thing they said. Worse, sometimes they say nothing interesting at all, and my mind just begins to wander, resulting in me never even beggining to pay attention to them.
Now, keep in mind, this doesn't just happen when someone is talking to me. More than once I've drifted off into programming concepts, women, and odd perceptions of the universe when I've supposed to have been taking a biology test. Infact, it happens in bio class more then anywhere else, because biology doesn't interest me much beyond the realms of the human reproductive anatomy (And my theory that all life can be described as a self sustaining chemical reaction, which I drift off into thinking about more often than not).
This wouldn't be all that bad, I can live with a C in bio for now, if it weren't for the fact that it's really obvious when I'm thinking hard about something. I have no idea why, although I suspect some odd physiological process, but when I think hard about something my forehead twitches. Once someone gets to know me they usually pick this up after awhile and figure it out, resulting in me getting slapped on more than one occasion. Try as I must, my forehead continues to twitch, sometimes even appearing to give off odd expressions when I'm thinking about an especially difficult problem.
I think I may have found the original cause of the problem. Multitasking. Yes, that's right, my ailment is the result of multitasking operating systems. They cause me to think about multiple things at once, spreading my focus, but making it thinner. Somewhat like elastic. Of course, multitasking means I can hide certain programs in the background, or minimize them so I can focus on the hardest problem. So I minimize whatever I'm supposed to be doing and start thinking about some odd mystery of the universe.
I can't decide if this is a blessing or a curse. It certainly doesn't help my social life, but it does help me focus on what I consider important. Perhaps I just need to rearrange my priorities...