1. What if you loose that one card? While on safari in central Africa?
Nothing for 500 miles?
2. What if the card breaks? While on safari etc.etc. It happens.
3. What if you forgot to take off the 799 shots of Brittany Spears
f#%&ing the mailman you happened to be in a position to take, and
Sasquatch walks by? Do you format the card?

Seriously, I carry a 512MB (~150 pics with my camera on "super-high
quality" JPEG), and a 256MB and a very old 96MB as spares. And I've
used them all on numerous occasions.

Also, you might want to increase the resolution of the pics you're
taking, if possible. You only get one chance to take a picture; you
should make it as good a shot as possible (within reason, of course -
RAW may take too long). You won't get a chance to go back and shoot
that exact same moment again.....

ECM