Here's something to help you make your mind up. As I said earlier - its still Timeshare, and you haven't really a prize because EVERYONE WINS THE PRIZE.
http://www.consumeractiongroup.co.uk/forum/hol iday-companies/37585-clubseasons.html
What the timeshare industry does is to sell of the unused capacity by using the technique you are being sucked into. Having got you captive on the site, they then attempt to sell you a timeshare unit.
However its not all bad news - it is possible to get access to this spare capacity by renting out redundant weeks directly from the resorts. Management of timeshare facilities varies an awful lot but some resorts that are under the control of the owners provide this service to their owners - you can get a week for roughly the price of the weekly maintenance fee. This is one such management company operating in Tenerife (mainly).
http://www.wimpen.com/default.htm
You'd have a make a rental request to them - this is one such company, there are dozens