For D-type connectors I normally drill four holes for the corners, then as many holes as posible untill I can bang the middle part out with a hammer, then I fle the rough hole smooth.

I drill usually 4 holes in the corners and use a cheap Black & Decker reciprocating saw to cut between the holes.
Than a flat course file to file it smooth and a fine square file for the corners.

And otherwise the same as Hero999 suggests. drill holes and pop it out, than file.

For round holes i use a stepdrillbit, or holesaw.

Well I bought a rotary tool..

This one

Its a Mastercraft and was half price!

Came with everything I needed

For my first attempt I cut out a slot for a db-9 connector..

It turned out alright.. i wouldnt say it was bad but i also wouldnt say it was good.. seems like it will take a little practice to get good.

I didnt really know what cutter I should use.. I tried using one of the cut-off wheels.. it cut but it got so hot that it was melting the plastic

I then used a teethed cutter which did the trick.

The kit did come with a diamond tipped cutter.. might try that next time.

The aftermath of the cut was pretty nasty looking so I used one of the aluminum oxide grinders to smooth things out.. next time I might just use a metal file for more control..

overall its a pretty good tool.. need to aquire the skill though.