On a recent Colorado trip I tipped the guide $40 for the day, and in all honesty he was reluctant to accept it. As others have noted this was cash to the guide at the end of the trip, not to the shop. I took the time think about the tip ahead of time and brought two $20s with me. Had the guide been a jerk he probably would have only received a $20 tip, but as the guide was excellent he received the full $40.
Like Ed I have friends who are guides and know it can be tough to make a living through guiding, so while the trip was expensive the tip was just a planed part of that expense. To those who complain about guides being jerks, etc. my experience is those types tend to gravitate towards certain shops/outfitters, and avoiding those will generally ensure an excellent guide.
Brian
"My father was very sure about certain matters pertaining to the universe. To him, all good things - trout as well as eternal salvation - come by grace and grace comes by art and art does not come easy." Norman Maclean, A River Runs Through It