An interesting live scenario for this matter: http://www.bondfaro.com.br/ (brazilian site)
The query "ipad" returns results spread across many categories (links on the left, teasers in the center). The "Tablet" category (facet) is one of them. The query "tablet" does exactly the same as clicking "Tablet" in the search for "ipad". Note the breadcrumb (Início>Informática>Tablet>tablet) In this case of a broad term, that exactly matches a product facet, it totally makes sense for the user. In general, it tends to make more sense as the search bias from full-text to structured metadata. So, is it possible to turn "q=cardiologist" into "q=specialities:Cardiologist" by boosting an exact match on a facet label?
