Between 800–1200, more if it is a large wedding and reception. This does not count any pre-wedding sessions with bride, groom, wedding party. I will shoot more at outdoor weddings, usually because of my doubts about lighting situations.
Nimis nails it about whittling down the shots. I will do my whittling, then let my wife do some whittling (she sees things with brides that I don’t, then let the client do their whittling.
I’ve never had a card crash, but I have made stupid mistakes when downloading images. So, I do the multiple card thing as well. I also use a good point-n-shoot to shoot a couple of hundred shots. Guess I am a belt and suspenders guy when it comes to weddings.