Has anyone been to one? Anyone from Massachusetts going?
Yes, we attended the 2001 edition hosted out of Hood College in Frederick, Maryland. Didn't care much for the dorm room accommodations and it proved to be a wet weekend, but overall it was a very good event if only because of the people with whom we shared our weekend rides and meals. We have since been to a few of the MATES rallies -- also put together by ETR, Inc. -- and may do so again just so we can meet up with old friends from the previous ETR and MATES events. I believe this year's event is being hosted out of a resort as was last years; while a bit more expensive they "should" be a bit more comfortable accommodations.
As for riders from Mass., we met two or three couples from Mass. who I believe are "regulars" at ETR events. In fact, two of the couples are headed this way in April to catch the Tour de Georgia. We hope to cross paths with them at one or two of the mountain stages.
Anyway, it suffices to say, a good rally is one that is well organized with nice accommodations, good food, and nice routes with some local points of interest tied into the weekend. The difference between a good rally and a great rally -- cost notwithstanding -- are the weather and most importantly of all the interesting people whom you'll meet there and perhaps find added to your list of tandem friends.