Mules?

[Cliff Fenneman <cfly@concentric.net>]

Why do you suppose more people don't use mules for endurance?
I'd be interested in what your impressions or what your experiences have 
been.
I'm starting a mule with the intention of eventually, her replacing my 
wonderful Arab.
. The mule is extreemely strong, very fast at all gaits, very 
intelligent, sure footed and competent on the trail, and she is also 
more agressive and feels slightly potentially dangerous. She has great 
PR's too.
So, why don't more people use them?
Comments?
Lynda