As I’ve been taking more and more pictures with my camera (Nikon 5700) I’ve come to realize that its not worth reducing file quality. I started shooting at 1024×768 and have moved up to 1600×1200 as my default size. Even though it still isn’t full size on my camera I find that 1600×1200 is a good compromise between size and quality. On a 256 MB card:

Depending on the compression ratio and what size CF card your using add subtract to find out how many pictures you can hold.
When the camera is set on Fine Mode I can take a total of 260 pictures at 1600×1200, which is usually more then plenty for a day. On longer trips when I dont have access to a compter, instead of turning down the resolution I’m thinking of buying a ImageTank. Roughly $250 dollars but they hold 20 gigs of pictures, which would be like 40 completly full (256 mbs cards). Works out a lot cheaper then buying twenty 1 gig CF cards.
Now if only Apple would come out with a CF card to IPOD converter : )