Multi-Project or Single Project

In many areas of my life, I enjoy the efficiency of moving from uncompleted task to uncompleted task, as I get bored or hit a mental or physical stop.

I am cursed with rather a multitude of web application ideas, and the sheer number of them would dilute my efforts to such a point that I would never accomplish anything, were I to allow myself to float among them. In self defense, I have implemented a policy of finishing one, to at least a beta level, before I get to start the next one.

I feel that this is not optimal though, as the parallel task approach really seems to work well in other areas of my life.

Do any of you work on multiple projects of your own simultaneously? (Work doesn't count, as there are deadlines imposed by others at work, where our own projects have deadlines imposed only by ourselves.) How many software projects do you work on at once, and how did you arrive at that number?