I had an interview Friday afternoon and among the hoops I had to jump through was a series of four tests.
The first was supposed to evaluate your visual logic skills (I forget the correct term for that, sorry.) Take a look at this:

That's not actually from the test, I threw it together in Corel Draw tonight using the same puzzle form. It's probably a little easier than the real test (which had several different diagrams and the operations for each symbol changed each time.) The actual test was multiple choice, but I didn't look at the potential answers until I'd arrived at my own answer, so I figure you guys are smart enough to do without! :-D
(Plus I'm too lazy to come up with some answers.)
Pretty simple, really. But under pressure, not such a walk in the park. Anyway, if you've got that brain-itch, give it a go.