I find that I cannot work on more than one project at a time. It's tempting to try, but whenever I do try, I get completely blocked on all projects.
How about you? Have you ever revised one novel while drafting another, for example? Do you write a short story half-way through, set it aside to write another, and then go back and finish the first story? Do you think you can get the same result from multi-tasking your projects that you would get if you worked on one at a time?