I treat it all as karma.... i've been blessed with supportive family and enough intellect to have a comfortable lifestyle. Though i don't open my wallet for every tip jar I see, begrudging an extra buck or some change here and there seems petty and i'm happy to share my good fortune with those who are working to take me places, make me comfortable, or otherwise serve me.

As for waitstaff, having waited tables and bartended my way through my own six-figure education, including working nights the first two years to augment my lowly initial professional compensation, i know that i personally worked very hard to make sure that people had a great time and experience when seated at my tables or bar. That said, I knew damn well that the cash i was able to earn at those service jobs beat nearly any other option i'd have had at that point... by working my way into top scale places I was making more, $30+/hour, working 3 nights a week than i was at my day job. To me, THAT was disgusting. My last summer waiting tables I upped it to 5 nights a week and saved up over 10 grand to pay off the balance of my student loans before switching professional jobs.

one other thought regarding the percentage based on sales (that is, a waiter getting 15-20% for selling higher priced items, etc.).... in some ways you have to think of it as a commission. The waiter is effectively a sales person for the restaurant and so it's similar to compensation for a typical sales role, only the customer is paying it (somewhat discretionarily). If it was added in advance and you didn't see it, they would likely still be compensated on this type of commission basis. My favorite trick was selling $40 lobsters; the restaurant would only stock 3 per night but i would often be able to sell all three to a table of businessmen on expense accounts having a pissing contest by telling them about the special "but there are only three left so you have to let me know right away if you want them and I'll run back and save them" - when i spotted the right table this ploy would work close to half the time. Ka ching, there goes my per head for the night (this was a place with average main courses in the low 20s).

Probably getting a little OT here, but if you really think about it, compensation is based tyically on just a couple of variables: you can be compensated for your time (no one wants this b/c it's finite), your knowledge/skill, taking the right risk, or perhaps your uniqueness/rareness (though this is somewhat a subset of knowledge/skill). I pay our head of sales 25% commission on the gross revenue he brings in. This is somewhat a compensation on skill/knowledge, but honestly he is replaceable so I see it more as a risk play... he's risking earning nothing. That said he will pull in a half million this year but i don't begrudge him a penny because he signed up and took the risk and made it happen. He is not curing diseases, contributing to world peace, or really any other macro societal contribution other than making the world go around. Nor am I. My value as a human does not increase because i have acquired the right knowledge or taken the right risks to be well compensated for what I do, so I find it difficult to make a value judgment about someone else 'deserving' a tip or not. I suppose this is where i circle back to karma and my general sense of feeling good by being able to share, in a very small way, my good fortune with those i come into contact with.