Was just perusing the new Crystal 2008 brochure and most resorts ,Vail,Lake Tahoe,Winter Park lift passes say valid for 6 out of 8 days but not consecutive.It also seeme to apply to some Canadian resorts. Aas you say Pete, Killington allows consecutive days.
Worked for six years at a resort in Utah. If you are a skiier def recommend Alta. Can't go wrong with Utah. 4 resorts close to Salt Lake City. 3 resorts in Park City. Having said that my brother lives in Tahoe and it is awesome. Something for everyone for sure. If you are not fussy it is good to go to the smaller resorts (they are still big) as you save money and get more runs in (fewer people) and then go to squaw for a day.