I highly recommend that you do not rely on single large memory cards in your digital cameras. Not only will they be less compatible at camera shops, but, in my opinion, the bigger issue is that flash memory is not stable enough to hold my precious memories.
I work in this industry and have seen an unbelievable amount of Compact Flash cards get corrupt and people lose all of their pictures. I think a safer solution is to get a few smaller cards so "all your eggs are not in one basket." You should also burn CDs of your images as often as possible.. don't rely on hard drives either as they are also prone to crashes.
Just my two cents...hope I can save someone some angst!