It seems that 80% of this thread is people saying how evil not tipping is, and another 10-15% of it is people agreeing with them.
I think the numbers hold true that 90-95% of the board thinks that tipping is a wonderful way to reward good work. I couldn't agree more and enjoy giving generous tips whenever I go out.
The real discussion is of two groups: 'what tip is appropriate for a decent day of guiding?' (averages to about $50-100 as the most common) and 'why do guides commonly charge a price that does not reflect the actual costs and income needed for a return?' (because that's just the way the service has always been run)
I, personally, would much prefer the system Pcray has suggested, where a tip really is gratuity for an excellent job and initial prices are much higher. That's not the current culture, however, so I'd be ready to pony up between 50-100 dollars or more for a tip on a half-day guide.
If I expected to return within a year or two, I might just double that tip, which is what I do for most other venues I expect to return to.
Can we stop harping on how lame/evil non-tippers are now? It's such a minority here that it's not worth having most of this topic devoted to it.