This also reminds me of a story in the StackOverflow podcast (https://stackoverflow.fogbugz.com/default.asp?W24222), where programs executed as expressive bytecode ended up outperforming machine language programs on a low-memory machine, since the more verbose machine code executable was so much larger that parts of it had to be swapped from disk.

Not really at the same level of bit-tweaking as the XOR lists, but a nice bit of counterintuitiveness still.