anybody interested in discounts?

How useful are these discount cards? I was recommended the VIP Backpacker card by STA over other discount cards that were available and I'm struggling to make it work out. Hostel sites seem to be priced pretty much exactly the same on the VIPBackpackers site as on other sites such as Hostelbookers... has anybody found any genuinely excellent deals with these things? They can be used for trips, tours, transport and hostels so there has to be a way to get back the £12 (varies depending on card) fee?