My favourite buffets are the ones in Asia, usually Sunday brunch, that include free flow champagne or wine. At these, the answer to my own question is usually "a lot"

Singapore has some excellent ones, any time i am in Singapore I try to be there on a Sunday to enjoy one of these.

I have also had the pleasure of an excellent champagne brunch at the JW marriott in Shanghai, and slightly less posh, about 8 years ago in Vietnam various hotels offered them for around US$25 which included unlimited food and free flowing wine!

Suffice to say, the food was not my primary concern at many of these buffets , although in Singapore certainly the food tends to be of a high standard