I've only once hit an auto-tip where it wasn't for a large party AND explicitly called out on the menu, which was (surprise surprise) at a touristy place in NYC, although a relatively moderately priced one.

I complained to the waiter, who said it was policy, and asked if I wanted to talk to the manager. I didn't bother, since the precomputed amount was less than I would have tipped otherwise -- can't remember if it was 15% or 18% but amazingly, it was correctly calculated on the pretax.

If it were a place I'd have ever been likely to return to, I'd have made a stink with the manager and then tipped what I'd have been originally planning to. Since it wasn't, I didn't bother; the place was inexpensive enough that the difference was only a buck or two.

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Speaking generally, I tip a little over 20% at inexpensive places (20% on the pretax, round up to the nearest 50c or a buck if the service was good), and use the "double the tax" rule at moderate-price ones, which comes to 16%-17.5% depending on which city I'm in around here. At expensive ones, it depends entirely on the service, but defaulting to actually calculating out 15% if the service was merely OK.

What's everyone's "minimum tip"? I generally won't tip less than $2ish (e.g. if the bill is something like $8.03, they'd get a $10 left for the bill and tip.) Not too many table-service places that cheap left, but where there are I don't feel right leaving less.

For buffet and counter-service places where you don't clear your own table but they don't take drink orders, I'll usually leave a buck (or a buck a person when there with my wife) for the guy who clears tables. Vegas/Reno buffets where they do drink orders at the table, I'll generally tip $5 for my wife and I if they're good about refills.