I only keep the really important ones... like cards from my 78 year old grandmother. Everything else (including pix most of the time) get thrown out. I'm soooooooooooo not a packrat. It's not just cards. I throw everything away. I figure if I haven't used it in a year and it has no sentimental value, it's just clutter. The only exception is Ben's stuff. If we have another boy, I'll want that stuff again. If we end up with a girl, I'll be getting rid of most of his stuff as well (keeping only the clothes that have sentimental value, of course).
Edit... I usually scan pix before throwing them away.

Didn't want you to think I was totally heartless.