Tips for cutting into acrylic?

[chadandjody]

Any tips for cutting a square hole into a sheet of acrylic?

[Knievel]

Not sure why you want a square trackball hole but if you have a router it's the best for working with acrylic/plexi.
I would make a template with a hole sized the way you want it in a scrap piece of MDF. Then clamp your plexi over the template, with the hole in the required location. Then just plunge through the plexi using a router with a straight plunge bit, run it around the perimeter of the hole and you're done.

[chadandjody]

The trackball kit I bought has a black mounting faceplate on it that fits around the trackball.