We have been members since 1993 and have used our points all sorts of ways (WDW, cruises, HHI and Interval exchange).
Our only Interval exchange was to Keystone for a week at Christmas last year. The resort was gorgeous and we were right on the slopes. At the time I felt it was worth it but after really looking at how many points we used I started to doubt myself. Because our stay crossed into January of 2009 we had to make two different reservations (Disney did not have a points chart available for 2009 at the time we booked the 2008 portion of our stay). I am now under the impression it would be more valuable to rent the necessary points and use the cash to book directly with the resort. When you do an exchange you don't always get the perks you can negotiate with the resort (food, ski lift tickets, golf, etc.).
As for the
Disney Cruise, each time we have done it we swear we wont do it again because you do use up a ton of points. When we look at booking direct and paying out of pocket we usually fall back into using our points.
I guess it is an individual decision!