My wife and I went to Las Vegas and spent 3 hours at the Hilton Grand Vacations showroom getting the full run-down on their plan. In the end we said no (and they were NOT happy about that), but it's because we are trying to get 100% debt free at this point, not adding to it. Their financing was a joke too (12%+ interest), but I wouldn't do it if I couldn't pay cash anyway. It's also an ownership deal where you have a title to a certain property, not just a timeshare (I don't know how this compares with other companies).
The best part of the Hilton deal was being able to roll unused points from the "timeshare" onto your normal rewards card at a 20:1 ratio, which means they add up fast, and soon you no longer have to pay for hotel rooms at ANY Hilton in the world.
Cheapest program they offered us was $12,500 for the equivalent of 20 days every 2 years. Next step up was $28k for 30 days every year.
The math works for us and how we travel right now, and as a "retirement plan" of sorts, we just didn't have the $$$ at the time to do it and it's not something I want to finance. But, we got a 3 night stay in Vegas for $100 out of the deal, and they did sell us on the plan for some time in the future.