I'm not sure what you're getting at with "useful," but it looks like it's going to be incredibly fun to play with, and I wish it were available when I was a kid messing around with HyperCard stacks.

I spent an hour trying to implement a 2d Turing Machine. http://www.puzzlescript.net/play.html?p=6863139 So far, it is unsatisfactory because I do not know how to emulate an infinite playfield, and I cannot figure out how to put a delay between applications of the rules (so you cannot see it running). That said, with a little tinkering, a Turing machine is possible.

With some help from Mr. Lavelle: http://www.puzzlescript.net/play.html?p=6869133 Hold X to run the Turing machine.