It's not really the 'most challenging', but the thing I hate most is minutes!  I like attending the meetings and getting the low down on what's going on, but it's so boring having to relive them and make sense of some of the ramblings!

Organising travel is a pain, especially when there are last minute changes, but it can be quite interesting.

For me I think 'most challenging' has to be organising the xmas party - you try to please as many people as possible, but there's always someone moaning about it.  Usually by the night of the 'do' I've had enough and don't want to go (but I always do)!  It's going to be time to start organising again soon - aarghhhh!