I first started out with
Spinsanity's lazy kate. It might work well for someone who spins thick, but I spin laceweight singles, and there's not enough drag to prevent massive tangles and snarls.

However, I found that it works beautifully for winding singles onto a bobbin. I inserted screws into the PVC bobbin caps, rigged a shoebox to poke my spindle through, and use my electric drill to wind on.

That left the problem of needing a good system for transferring the singles from their 3 bobbins into a ball or 1 large bobbin for plying. So this past weekend, I added a second lazy kate to my collection -- a box from Target that was laying around and some old knitting needles.

It works perfectly! I put the large bobbin on Spinsanity's lazy kate and used the drill to wind on the 3 singles, then I put the large bobbin in the new lazy kate and plied from that. It was flawless! No snarls, no tangles, even tension on all the singles... I'm thrilled!