I also believe strongly in thank you's.. BUT the best ones are sent because you sincerely want to thank someone, not because it is required or etiquette. I love sending thank you's for little things all of the time.. thanks for dinner, thanks for coffee, thanks for listening when I was upset the other day... etc. You never realize how much it may brighten someones day.
As for the wedding ones- I understand how they can get tricky- but I think the important thing, whether it's a card sent in a timely manner or not- is to make sure you thank the people who were there for you and gave you gifts in whatever personal way best suits you, them, and the situation since all are different.
All I mean really is- don't forget the root of the reason you are sending them!