Too Many Cards?

Z-man's new release Parthenon comes with over 400 cards. Trivial Pursuit comes with several hunderd question cards. The Apples to Apples crate comes with several hunderd cards, etc.

You need as many cards as the game needs. Basically, you have too many cards when you can achieve the same effect with less cards. Do you really need 100 different event cards? Is the game less fun with, say, just 50 event cards? 25? Maybe you want even more than 100. Only you can answer these questions.

Production wise it is most economic to produce cards in multiples of 55. That's why you see a lot of card games with 55 cards, or 110 cards, but not so much games with 80 cards or so, because that means a lot of cards would be "wasted" during printing. I wouldn't worry about this too much when creating a game though, unless you are specifically trying to create a compact card game.

This is a slight overgeneralization. It depends on the sheet size of the manufacturer really. Many have 110 card sheets, but not all. It is really useful to do a game in multiples of your sheet size OR to fill out the unused sheets with promotional cards that you save and handout at a later date.