Christmas cards get hung up on a string running between the beams in my house between my kitchen / living room and remain there till new years, then they get tossed.
Birthday cards get left on the table/mantle/desk/wherever I feel like it, on display for the rest of the month. Then get tossed.
Any other card is read, placed on the whatever area and left there for a week or two then tossed.
Sympathy cards are read, placed on the whatever area then destroyed once the person leaves my home/
They sit on the table for a week then I throw them out.
Unless...they are from the girlfriend, then I save them. Personally wouldn't save them all, but I do. Typically women want to know/think you care about these small things, so her knowing I saved them all might mean something to her someday.
I once kept every letter, card, and personal note I received.
Then, one day, I threw nearly all of them away, keeping only the "important" ones (first birthday, last card from departed grandparent, that sort). These days, I can't quite justify keeping most cards since I've already thrown away papers that were more important to me.