My understanding is that you can only get the 50 Disney dollars if you book a package. I can't speak for those traveling to different resorts or at different times of the year, but for us booking a package would have been far more expensive than making plans a la carte. This is especially true because we are staying at a budget resort (***) which only has discounts during value season. I was lucky enough to get a different kind (not DC) of discount applied to my peak season reservation, and if I were to switch to a DC package I'd be paying rack rate for the room.
Because we already knew we were planning a trip for this year, I went ahead a paid for the DC membership, but I won't renew. Because I bought park hopper tickets at a DC discount months ago (before the 2001 rate increase) I did save enough to pay off the membership.
But, otherwise, compared to the much better discounts that used to be offered as part of the FREE (though my office) Magic Kingdom Club, the discounts offered by the DC are pretty sad. Hotel discounts are much less available than they used to be, as are restaurant discounts.
Unless I'm mistaken, there are almost no dining discounts left in the parks themselves and the merchandise discounts that remain in DD mostly have minimum purchase requirements (NOT the way MKC used to be, I think). The decent discounts that remain (Disney Quest, water parks, etc.) are almost all also available if you have an AP or AAA or AmEx.
As for the Entertainment discounts . . . I thought that was great, but now it's starting to seem that, while there are benefits, that they may be somewhat limited compared with "normal" Entertainment benefits obtained by buying the coupon book.
Mine has paid itself off in ticket discounts, but, otherwise, has done me little good. I'm glad to have one more discount option to try and use on our trip, but I do think that you have to work at it to get a real savings.