Depends on your camera and the type of card it uses. My Sony A200 has a Sandisk Extreme III 4Gb memory card in it which is capable of 3 frames per second for at least 50 frames (haven't held my finger down any longer than that). The older memory cards are slower.
The main issue I have with large memory cards is, the more photos per single card the more there is to lose if you
a) lose the card
b) corrupt the card.
That is a very valid point. I have 5 cards from 512 kb to 2 gig. I bought a card that came with a nice holder which can store 8 xd cards in a wallet.