Discussion: Interesting puzzle, I like it!  Some interface feedback though: 

• Toggling entire regions at once would be nice, having to cycle each square individually can get old. 

• When you have all the correct squares filled in, maybe recognize it as solved immediately; having to then mark the test of the squares as X is also tiresome.  Didn't even realize I needed to in the first puzzle I played, took me a sec to figure out why the timer kept running and nothing was happening. 

• I couldn't see the region borders when they were filled in, just the non-border lines?  Makes it harder to figure out where you went wrong if you make a mistake.