Useful HR Zone feature on mentoring here:
http://www.hrzone.co.uk/cgi-bin/item.cgi?id=167729&d=1063 .

I think it makes a few good points:

• mentoring isn't just for newbies
• mentoring is about being a sounding board not giving advice
• being a mentors is a good way for people to experience career development even after they have "peaked.

All in all a very worthwhile contribution.