Decanting

[wondersofwine]

I'll try to answer only the restaurant part of the question because personally I don't do much decanting at home. A serious wine connoisseur (sp?) ordering an expensive wine at a restaurant might arrange with the sommelier to decant the wine ahead of time. This would require deciding ahead of time what wine will be ordered that evening and phoning in the request. I imagine that this occurs less than 1% of the time even in fine restaurants. Also, even though older vintages may be more expensive, they usually aren't decanted in advance because if they are past their peak, they may deteriorate quickly once the cork is pulled.
Probably in most cases the restaurant diner settles for letting the wine evolve in the glass during the course of dinner or perhaps requests that it be decanted when ordered, not in advance. (I also don't think most restaurants would have enough decanters to put one on every table drinking red wine).