I think Archipelis 3D is the only actual 3D editing program so far for the iPad. Archipelis 3D is something I used on my PC and it is simple to use. The iPad version interface and operation is almost identical and it was a weird experience using my finger instead of a mouse or graphics tablet to trace around the picture I was using.
Alas, the enjoyment ended when Archipelis 3D locked up solid and froze the iPad up so I had to restart it. I tried several images and most of them low-res, but the program still eventually froze.
Reading the specs for the iPad, I think the amount of RAM is just too low for 3D graphics work on the iPad. It was worth the couple of dollars to try it and it could well have been a winner if it worked.