Fascinating - inabiity to multi-task is often cited as an Aspie trait, yet there appears to be little evidence that human multi-tasking really exists:
http://en.wikipedia.org/wiki/Human_multitasking
I seem to be able to perform one main task and slip in a few brief, simple operations during slack points in the main task. If I have to wait for something to process, I can get a bit of other stuff done in the meantime, but I find it's risky unless I set a timer. Even on that level, I find it can reduce my effectiveness because attention to one task can remove my attention from another at a point where it's not really a "natural break."
I suppose, inasfar as multi-tasking is possible at all, I'm probably worse at it than a neurotypical, because I have the Aspie difficulty in picking a job up again after I've been distracted. I'm a lot happier if I can just do one thing at a time.....often I notice limitations even when doing that, because a single project will more than likely involve a number of sub-tasks, which I have to flip between. And I tend to get more ideas occurring to me than I have the time to explore, they kind of "bottleneck" and I try to hold onto them all, which is distressing.
Obviously there's a big difference between well-learned tasks, such as riding a bike, and tasks that require the application of the conscious mind, such as reading a new document. The former is much easier to run alongside other tasks, as long as nothing goes wrong.