We became members quite a few years ago, and have enjoyed many great vacations.
Pro - Great accommodation, right onsite, Disney quality, flexibility of dates and places to stay.
Con - Ever-increasing dues - We get a bill every January which this year is close on £1000. Add to that the flight costs, meals and spends, and it's an expensive holiday, even staying on points.
If you have a spare £20,000 in the bank, it's probably still a good deal, but do your sums!