Don't think there is one. I frequently send mine back as well. I'm sure there are some who will see the card as a way of keeping track of guns and owners but that is already done . S&W has even given some gift certs post registration.The issue of warranty coverage aside, I have had mixed feelings over the years regarding whether or not to send in the card and associated questionaire that usually accompanies it.
Many people have concerns regarding additional 'registration' type info being maintained, and on a certain level that may be valid, but does not bother me for Walther to have my name and address.
However, on the up side, when I have sent in my registration cards for some S&W purchases, have received some nice benefits back. Seems like it keeps me in the loop on some factory info sometimes, also, recall getting a $25 gift certificate for S&W merchandise, got a couple of nice white shirts with the S&W logo out of it.
Would also seem that the factories may use some of that demographic and preference info such as reason for purchasing that particular firearm, in making decisions on their next product to release, would think that kind of info / feedback from consumers to Walther might be helpful for everyone.
Just my thoughts. Have not sent in my card yet that came with my PPS, but probably will soon. If anyone knows of any significant down side, I would be interested in hearing. Thanks.