One more question (for Maitre D in particular, but anyone else is welcome to answer):

I know it's been discussed before, but I don't believe there was a consensus: should we always tip on the "pre-tax" total?

Usually makes minimal difference, but with large bills, it's an important decision.

Opinions seem to vary widely--on separate occasions, I have been laughed at for suggesting either convention (and accused of being a gross "under-tipper" and "over-tipper" respectively).

Thanks.