I would add:

- do they communicate about their work?

For me, that's number one. Often, really smart programmers are really terrible at communicating about what they're working on. They get into Lone Ranger cowboy mode and write tons of code without telling anyone what they're doing. They may get a lot done on their own, but it makes them nearly impossible to work with as colleagues. If I had to choose between a coworker who wasn't very good at coding and a coworker who wasn't very good at communicating, I'd gladly choose the one who isn't very good at coding.