My wife and I have been doing these cryptic crosswords - we usually do one a night as we're trying to coax Sofi asleep. They're very satisfying once you start figuring out how to do them - the first few we did we couldn't make head or tail of, but after looking at the answers we started figuring out the tricks.
Interesting thing about them--and I haven't done tests to prove this scientifically, but I'm pretty sure it's the case--it takes two people less than half the time to solve a cryptic crossword than it would take one person. (This is true for regular crosswords also, I'm pretty sure.) Each answer gotten lays the groundwork for future answers, so we're accelerating each other through the project.
Which is the opposite of Brooks' law. So there are situations, such as solving crossword puzzles, where it's not true. Another example: an artist and a coder can get more than twice the game made that just an artist or just a coder can.
And sometimes you put two programmers together on a single machine because two together can outperform two by themselves.