If I'm working with strips--they can hang out of the way on the wooden ladder, so I have room to work on at least two at a time. But, I'm working on one now, Kayak on the Lake, and it requires all these piles of triangles to be laid out so I can choose colors carefully. The piles are all over the ironing board and the one small table top. I was going to start another--but there's no room to fit more pieces anywhere. Rats! So--for the moment--one at a time, but that's not the norm.
Once school starts (teacher on summer break), my quilting time diminishes greatly, so to remember how to piece something, I'll often work on ragged flannels and one other more complicated project.
I love to make tops--and hate the rest--unless I'm handing it off to my quilter... but I'm proud to say there's only one unfinished project now. I finished the last binding on an unfinished piece tonight--finished the last three this week. :D :D