Every time you click on a checkbox the permalink is change according to the permission, so its easier to copy the permalink.
Therefore when you click the back button you're going to the previous state.
Neat. I suggest adding an explanation of what the special bits do (tooltip type of help on clicking the link?), as this is what's not obvious for most people.
Yeah, same problem here. At first I thought he had skipped out on allowing you to type the mask, which is the killer feature of a utility like this.
Also, when typing into the binary input, it isn't updating immediately on key-up like the rest of the inputs -- I'm having to hit the arrow keys to get it to update.
This is pretty cool and well done, but I kind of wish there was no need for this to exist.
It seems that as the world progresses to higher level language, bit manipulations and binary calculation are the realm of dinosaurs.