Still wondering about the extract... (see my previous post) What are the differences between the different kinds and is one superior?
gives some information on the various types of extracts. I think most commercial extracts are made from the species Vanilla planifolia
(aka Bourbon vanilla), since the other common vanilla species, Vanilla tahitensis
(aka Tahitian vanilla), has very little vanillan, which is the major flavor compound in vanilla. I'm sure differences in climate, curing and so on make even genetically identical vanilla plants taste subtely different (i.e. by encouraging or discouraging the formation of different flavor compounds), but I'm not in a position to say what those differences are or how apparent they are to the taste.