My experience is that they work once. Having said that, however, I have noticed that some coupons don't come off the card right away (or even 24 hours later). Example - I had a $3.00/1 charmin e-q on my card. I used it once and thought that was it. About a week later, I noticed it was still loaded on my card. It actually DID let me use it again. Cellfire Qs seem to stay on there until they expire.
Bear in mind that it sometimes takes several hours for Qs to show as "redeemed" on your card, so you probably don't want to rely on multiples for several transactions in one day. My advice is to check the E-q sites often, and check your store card online often, to see what Qs are on there. That way, if a day passes and your Tide coupon is still on there, there's a good chance you can use it again!