I LOOOOVE my TIW card!
If you spend more than $375 at participating restaurants in a year, then it saves you money.
Here's a list of places that accept it:
http://allears.net/din/tiwlist.htm
Keep in mind that very few CS locations take TIW. It's mostly just for TS restaurants.
There is an 18% gratuity charge automatically added to your TS bills. So I basically look at my savings as not having to tip.
So, an example:
Check is $100
20% off is less $20, bringing total to $80
They add 18% tip to the pre-discounted amount of $100, so $18...total of $98.
Tax on the discounted amount: 6.5% on $80 = $5.20
So a total bill of $103.30
Without the TIW card, and tipping the same 18%, you pay $124.50
Total Savings of $21.20
Another perk I love is the FREE valet parking at resorts. You still need to tip, but I look at it as $5 for valet parking that is normally $12 ($18 with a $5 tip!).
You just have to present your restaurant receipt showing the discount and sometimes your card when picking your vehicle up.
You also get around 13 months of discounts for the card. It's good for 13 months plus until the end of whatever that 13th month is.
So for example:
I last got a TIW card on 12/11/10. It is good through 1/31/12.