TomB: "I'd hazard an educated guess that the number of places which major specifically on traditional song (where you'd hear perhaps more than 80% trad through the year) to be only about 30% of clubs. (Note that I'm using trad to mean proper, old, public domain material, not popular newer 'falk' songs [falk = fakefolk ok?]"
...
"My personal experience of the much-more-difficult-to-quantify open mic/unplugged/song-session type of gathering would be that trad material would be less than 10%. Proabably a lot less."

Very interesting Tom.
30% for more formal venues actually seems a pretty decent percentage to me.
As for the other 10% in less formal groups, my personal experience would tend to match that estimate. With me virtually being that 10% *smile*.