The cesus seems to be:
Harps: Allan C, Sandra, Helen, Jen, Emily Rain, Susan of DT, Black Walnut, Sharon
Autoharps: Bill D, Rick Fielding, DDW, Harpgirl, Harpy, Susan of DT
Zither: Ferrara
Hammer Dulcimer: Paddy, Catspaw, Sharon
MacArthur Harps: Ferrara, Susan of DT, (and of course, Margaret MacA)
Other: Bert, Rick Fielding, Sharon
The preponderence of harps is probably more due to the thread title than to actual numbers. Other instrument's players may not have read the thread.