We deal with highly available systems and we have a very good team dynamic so we are somewhat picky but yea, these are some of the questions we ask and some answers we've been given. Mostly in the followup fact to fact interview. A majority don't even get past the simpler phone interview.
What software uses the following common ports: 20/21, 22, 24, 25, 80, 443 or we'd ask the reverse, what port is dns on, tcp or udp? What port is http (we've received 8080 for this one). Worse the followup question is, okay if you don't know what the port is where would you find it? A recent interview had the guy providing Google first then looking it up in his Network+ book.
The biggest issue we have I think is our offices are in North Denver and the Tech Center is in South Denver. So most tech folks are in Castle Rock, Highlands Ranch, Aurora, and around those areas. So commuting would be north through Denver. We do have IBM and Boulder up here so we should get some folks.
I think most admins might either be happy where they are, don't want to deal with the commute, or perhaps are looking at something beyond Unix Administration like VMWare, SAN, and the like.
We've interviewed folks from other states (Washington, Maryland, Ohio, New York) without much luck. We did bring one guy in for a face to face but he failed that (I wasn't in town for that one).
[John]