All,
Sorry if this is old news but...
The tri-tip cut of meat seems to be a popular Northern California thing...not sure how regional it is.
My girlfriend's family is from the Pacific Northwest and they had never heard of it until we had it at my place.
A really great way to prepare it is to marinate it for two days in Chaka's MMM Sauce ( I think this is a local thing, too)
http://www.chaka.com Absolutely the best on the BBQ for 40 minutes..turning it over every 10 minutes.
-Jeff