I have never done so, and they have never balked.
Past treatment of warranty claims of others should not, however, be your guide.
As a matter of information, I have noticed that many people do WAIT to send in the warranty card. I often see warranty cards still in older boxes when they are sold. Prior to online registration, S&W really had no way of knowing when you actually purchased the weapon, so the thinking was that you sent in the card if you had a problem. If you had no problem, you could sell with the warranty card intact so that the revolver had ALL of the paper, box, accessories, which makes it worth a little more.
The dynamics of that have changed with the ability to register online.