We have had one for years and we wouldn't change it!
We use the clubcard deals on-line NEVER in store. If you had £10 clubcard voucher and you use it in a tesco supermarket you get £10 off your shopping.
If you use that same £10 clubcard voucher on their deals you get 4 times the face value so £40.
I buy my annual £200 RAC cover with them, so it costs me £50 in clubcard vouchers, we use it for 2 day breaks in hotels and for days out to places like Alton Towers or Warwick Castle, magazine subscriptions, eating out in nice places with our boys etc etc.
You get more points using it in a tesco supermarket than elsewhere but you can also use it for Tesco Direct home stuff so we always do very well on the deals front.
I don't even shop in tesco but it is still well worth my while.
Pop onto their website and have a look at what you can spend your clubcard vouchers on
www.tesco.com/clubcard/deals/
look at the list on the left had side to see how many different things you can do/spend them on.