I think it's safe to say that we all find ourselves multi-tasking from time to time. For example, I'm multi-tasking right now. I'm writing this post and listening to a podcast at the same time. So how good are humans at multi-tasking? Unfortunately, not very good. There are several studies showing that humans are not able to multi-task two or more tasks at the same time equally well. I watched this very cool YouTube video from BrainCraft discussing this very topic and found myself nodding my head to much of what was shared.
BrainCraft - Multitasking
When multi-tasking we tend to switch back and forth between tasks. Thus we are not really multi-tasking but multi-switching. When multi-tasking we have a tendency to focus on one of the tasks and ignore the other. For example, right now my focus is on writing this post. I'm listening to a podcast at the same time, but not really paying attention to it. If you asked me what was discussed in the podcast over the last 5 minutes, I could give you a general idea but not the specifics.
There are, however, people who can truly multi-task specific tasks, such as running and knitting at the same time. Can these same people multi-task other tasks? Hard to say. There are people who can handle multi-tasking better than others, but those numbers are small. If I'm remembering the number from the video correctly, it is only 2.5% of the population.
In conclusion, I suggest we all face the facts. We can all multi-task, just not very well. :-)