escapee,
As a full time guide this is one of my least favorite subjects to talk about and one I never bring up, as a rule. I am quite often asked this question by clients as to how much or what is the norm on tiping. Makes Ya feel pretty uncomfortable when asked and is one of the reasons I put basic guide lines for Gratuities on my web site.
Basically in a nut shell what I put on my site is: "Gratuities are somewhat of a personal nature and should be gauged on your level of satisfaction. Over the years the average has been between 10-20% of your trip value. Again, this is only a guidline and know that whatever you leave will be greatly appreciated."