Computer memory has a life. It starts expensive, then gradually drops in price over the years until it is ridiculously cheap, then it is superceeded. In in few years time if you try to buy the superceeded memory then it is outrageously expensive.
Which brings me to 2GB flash memory. If you have an older camera -- particularly one that understands SD flash but not SDHC flash -- then the most it can take is a 2GB card. Those cards are ridiculously cheap at the moment -- $15 for a cheapo standard-speed card, $25 for a brand-name high-speed card. Now is the time to upgrade that puny 16MB SD card that came with the camera to the maximal 2GB card. Prices are so low that you can buy a fast flash card for double the price, and this seems to remove a lot of the sluggishness out of the older camera I own.
SD: "Secure digital".
SDHC: "Secure digital, high capacity".