Thanks for the link, Mav, I've added it to my favourites.

I think there's a time and a place for prescriptivism in any discipline, and language is no different. If you know the "rules" and understand them you are then at liberty to vary them in whatever way you wish, knowing as you do the potential penalties as well as the benefits.

When I first started studying economics I remember thinking that the definitions of the various types of market model we were taught were illogical in the face of everyday reality. However, when we got to the second year, the rules were relaxed and in the final year the rules were basically only used as starting points and not mentioned explicitly.

The same goes for written grammar, I think.