Capacity is one thing, reliability is another. I would feel uncomfortable with putting a lot of un-backed up images on a card - just because "stuff happens". I've already had cards with corrupted (on the card) images. While I did not lose too much, as I tend to shoot a number of variations on a shot, it still reminded me that I need to move the newly acquired images to a more reliable medium asap, preferably at the end of each day. I am currently using 8GB SD cards that give me the capacity to shoot a little over 260 RAW+JPG images, and I have four such cards with me at all times.
I have the same feeling about computer hard drives. It's really nice to have all that extra capacity, but the risk is that you lose a huge amount of data when those drives go bad. So having the capacity is wonderful as long as the users practice good backup procedures to allow them to recover from any loss of a single device.