Riffing off the Summerlicious discussion re: tipping, and resigned to the fact that tipping seems expected, here is what I do, and I'd be interested to hear what you think I SHOULD do and what YOU do in respect of this interesting and never-settled debate!
a) I don't feel the waiters' and auxiliary helpers' financial well-being is my responsibility. First and foremost it is theirs, with a close runner-up being their employer's. I regard my tip as a small extra reward for good service, with a variance upwards for especially good service and downwards for lousy service that stems from the waiter's performance, not from screw-ups in the kitchen and so forth.
b) The near-ubiquitous existence of tips' being pooled bothers me. I don't refer to the passing along of a small proportion of tips to busboys and maître d's and so forth, but to the massing of tips so that the same portion of the loot is divided among the front line wait staff. This destroys the most human (not always the most admirable, true) incentive for waiter X to try extra-hard to please my table, in hopes he will receive an extra reward. To me this is no different than a the bonus pool at a bank or law firm, and numerous other examples in business and professional life.
c) Paying an ever-higher tax to the nanny state I cannot avoid, but since it has nothing to do with the quality of the wait staff or for that matter of the meal or anything else within the control of the restaurant writ large, then I don't see any reason whatsoever to tip on anything other than the pre-tax total.
d) In a typical restaurant without a sommelier, I think of part of the waiter's routine duty is to open, allow me to taste and then pour the wine. Some restaurants' style is then to leave the wine on the table or in the bucket for the patron to pour. Obviously kudos goes to the waiter who re-fills the glasses as appropriate - which does not mean topping them up every few moments in hopes of selling me another bottle. So for a $30-50 bottle of wine the resulting additional tip is relatively trivial. But for more expensive wine - and for a restaurant employing a sommelier - I become more conscious of the 200-300 % markups over retail typical of such establishments, and think that the service of the sommelier and the provision of nicer crystal is rightly the norm along with other things for which one undoubtedly does "pay" in the cost of the menu items but for which one does not tip: say linen napkins or a stool for a lady's purse A particularly helpful sommelier who has spent time in selecting the right wines should have a few bucks pressed into his hand. But if I have chosen myself two bottles of Sr. Castellani's excellent Amarone thereby swelling the coffers of Le Select by $310, for wine that retails at the LCBO for $55 a bottle, thus $110, I don't see any reason to tip any percentage on the extra $200 that appears on the bill. The waiter still will - or won't - attend to the topping up of the glasses; and unless one believes the tip should be some sort of a sin tax on the basis that only "the rich" (which I am not) would order such wines, then I think the realistic conclusion is that his additional labour is nil. This becomes even more true imho when a truly "rich" patron orders several bottles of a $300-500 wine.
e) So given the above ruminations and conditions, and presuming I occupy a table for a couple of hours and order a typical several-course meal, I tip 15% of the pre-tax total, perhaps rising to 18% for truly great service or cheerful fulfillment of unusual requests, perhaps going a definite slice below for (rarely seen) truly bad and incompetent service.
Over to you...