I got one here at home...a Shop Notes Mag from 14 months ago (I read it while I was in the hospital waiting for Alyson to decide to emerge) that had a Panel saw in it. It was very detailed and had a deep laundry list of hardware that you needed for it.
Now I am a Fabricator/Machinist so I tend to look at things a bit differently than most...but at work we have a few panels saws and they look like they would be easy to build. Even the expensive ones use simple guides and bearings to get them to cut.
On a side note, my father made one out of 2x4's and OSB plywood that looks absuletly awful, but works. It has two modes to it. Use it as he has it and it is great for getting the plywood chopped down to size so it is manageable on the tablesaw for more accurate cutting. Or you can fuss with it a bit, clamp things with clamps and precision, and make a good cut with the skillsaw.
About the only problem with these rigs...my Dad's included...is that they take up some serious shop space. Space I don't have.