Writing several projects at once

I believe that no writer should bog themselves down with more than a few multiple writing projects.
The answer is really easy: You get confused.
It's easy to get bogged down when inspiration hits.  As a writer the fear of writer's block is always present.  The problem with taking on several projects is that they have a tendency to bleed into each other.  I like to write wherever my inspiration takes me, which leads me to different genres.  This can cause a major problem if you're writing a Science Fiction, Mystery, and Comedy all at the same time.  I limit myself to no more than 3 projects at once even though I have over 30 projects waiting for me to bring them to life.
Never rush your writing unless you are under contract to do so.  The more time you can put into your "babies", the better the outcome will be. I am writing ONLINE: the Motion Picture, which is the screenplay of my produced play; Brutal: The Las Cruces Serial Killings, which is a murder mystery; and another novel which is a best kept under wraps for the time being.  I am almost finished with Online but I make it a point to also add pages to Brutal and the other project as I feel inspired.  There will be plenty of time to rush yourself when you make it big and you have deadlines.  Now let the creative juices flow, even if they take a while longer than you'd like.
Keep writing down notes and ideas for your other projects though so you don't forget any of the wonderful things that will improve your creations.