Yep, they sure do. Typically up to five computers you can install on.
Since you both skipped it, the agreement actually doesn't limit the number of computers, only to the computers you own or control. The Mac App Store Terms and Conditions govern this, btw, so it hasn't changed for Mountain Lion, and applies to any application you download from the MAS, regardless of the developer or type of application.Yes. It's in the agreement you skipped.
Lion's agreement was something like "all the computers you control". I've heard ML's agreement was something like "up to 3 computers" but I skipped reading it too.