OK, I feel stupid asking this - but in Jeff's article: Getting the Interview Phone Screen Right and originally stated in the 5 essential phone screen questions:

They shouldn't stare blankly at you when you ask with 2^16 is. It's a special number. They should know it.

I've been a developer\software engineer\code monkey\whatever for a little while now, and I don't think I've ever come across this. I mean, I can certainly count binary values do basic operations on them, etc, etc. But I don't see what is "special" about this value.