I've seen companies have this policy and, on the surface, it seems like a good thing. You don't want to send a message that all your employees are male.

However, I'd be very careful.

• You're treating female employees differently: Some people see interviewing as an opportunity and others see it as a "punishment." Either way, you're offering an opportunity to one gender more than the other.
• Female candidates may feel you're pandering to them. It's a bit condescending to essentially tell candidates that they were given a specific interviewer because of their gender.
• You may actually treat candidates differently. Because you're using gender as a factor, you might be deemphasizing relevance, role, etc. Female candidates might end up with less senior or less relevant interviewers, for example, and thus it'll affect their hiring decisions.
  
• You'll likely put a disproportionate recruiting burden on female employees. It's a zero sum game. If I'm interviewing more female candidates, then I'm interviewing more people total or I'm interviewing fewer men. Both are problems. It's not fair or ethical to tell women that, because of their gender, they need to do more recruiting activities. It's also not great if men only get interviewed by other men.
  
  (By the way, this happened to me at Google. I was doing A LOT of interviewing, and I was told that one reason for this is that I was female. If you want everyone to be interviewed by at least one woman, then women may end up sharing a disproportionate share of the interviewing burden.)

My advice for companies would be to ignore this, unless you have pressing reasons to not. I think you're wading into a dangerous area and few women are particularly surprised to have only male interviewers. Avoid treating your male and female candidates differently, and avoid treating your male and female employees differently.

On a related note: when I interviewed at Google, the recruiter gave me a copy of "Unlocking the Clubhouse" (about getting more women into computer and reasons why women leave CS) at the start of the day, along with a Women at Google shirt. She meant well, but please don't do this. What a great way of reminding your candidates YOU GIRL, WE BOYS. It's fine to do some of this (some people will appreciate and benefit from it), but the start of the interview day is probably not the right time.