I tried using a Dremel with poor results. It's very slow-going and difficult to cut accurate curves and lines. The heat generated by the cutting wheel also melted the Sintra a little bit as it cut.
I also tried using a jigsaw with a wood-cutting blade, but it shook the hell out of the Sintra and and cut a very jagged edge. It also left little bits of plastic all over myself and my work area.
I finally purchased a plastic-cutting blade for my jigsaw over the weekend, and I'll be giving it a try within the next few weeks. Has anyone here tried that yet? If so, any luck?