Is there something similar to the Greasemonkey script system for a browser in iOS? Greasemonkey is explained in this Wikipedia entry.

I would like to add my own stylesheet to a particularly non-mobile-friendly website. Is there any way to accomplish this? Are there any browser apps that can do it?
At the moment there is the GreasePocket project in the works.

Have a look at their website, but it's far from a finished product, it will also probably need to be run on a JailBroken device.