I spent a lot of time looking at hornpipes for some rather complex reasons. The result was intended to be a diatribe which I wanted to use to assault the examination board who asserted that playing a 'simple folk tune' would only get a minimum mark. The outcome turned into a detailed analysis of the hornpipes in the Joshua Burnett Ms. 1840 (ish). As a result the paper was presented at the Fiddle Conference at SOAS in 2005.
Basically, the hornpipe is a much more complex proposition than merely 'dotted' or 'undotted' (although I expect you already knew that). It starts off in 3/2 then suddenly changes to 2/2 during the late Georgian period. It acquires dots much later and whoever noticed its self-destructive tendency to mutate into 12/8 is pretty much on the money. Its a real workhorse of a tune-type and deserves much more playing than it gets. How you play it is actually a product of your geographical and mental location - it defies description. Dave Shepherd called it the 'Quintessential English tune' and I think this is also spot on. Please feel free to visit my website and download a copy of the paper (.pdf)
http://www.hallamtrads.co.uk/research
cheers,
Paul