A. Your question made me smile, Helen, because I (and everyone else who falls in love with digital photography) went through the same progression. It's a very fun and rewarding hobby.
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You're very smart to begin thinking about backing up your memories. By now, you should at least have your iPhoto library of images backed up on an external USB hard drive. If you haven't done this, do it now. I'll wait.
Good. This saves you from losing photos in case your Mac decides to have a motherboard meltdown. But what if, God forbid, you had a theft or a flood or a tornado? I hate to be the bearer of bad news but hard drives die and, when they do, they give little or no warning. Poof! All your files are gone in an instant.