What if you don't have a writable optical drive or don't want to end up with your photos existing only in an iPhoto Library? You have a few options.
Other backup options:
Copy your iPhoto Library (remember that it's in your Pictures folder) to an external hard disk.
Use a dedicated backup program, such as EMC Insignia's Retrospect Desktop (www.emcinsignia.com), to back up your iPhoto Library folder (and while you're at it, I recommend backing up your Home folder, or even your entire Mac).
Export photos to folders in the Finder, then manually burn them to CD or DVD to back them up with your desired organizational approach. It's more work, but you get exactly what you want at the end.
No matter which backup method you choose, I recommend having more than one backup copy and storing one of them off-site. That way, should your house or office burn down or be burglarized, your backup would remain safe.
To reduce media usage (though CD-R discs are awfully cheap), buy the more expensive CD-RW discs and erase them in Disk Utility between uses.
Don't use CD-RW discs for true archiving, since anything that can be erased is a lousy permanent medium.
Don't assume that any backup media will last forever. Every so often, check to make sure your backups are readable, and it wouldn't hurt to recopy them every few years, just to be safe.
A Proper Backup Strategy
I'll be honest. I think backing up just your photos by burning them to CD or DVD is only a small step above useless. If you value the contents of your Mac, and if you value having a working Mac as a communications device for email and iChat, you need a real backup strategy. To learn more, I recommend Joe Kissell's Take Control of Mac OS X Backups ebook (www.takecontrolbooks.com/backup-macosx.html). It's only $10 and will help you figure out exactly what hardware and software you need and how to set it up.
I recommend that you select Verify Burned Data for safety; if you have trouble burning, try reducing the burn speed.
The options for erasing media and leaving a disc appendable apply only to rewritable media like CD-RW (but iPhoto won't erase no matter what; use Disk Utility).
The choice of ejecting the disc after burning or mounting it on the Desktop is minor, though I recommend a quick visual inspection of the contents of the disc in iPhoto after burning.
If you want to archive photos, that is, burn them to disc and then remove them from your hard disk, I recommend the following:
Make at least two copies and store one off-site, like at a friend's house.
Work methodically by making albums from film rolls to retain organization and by selecting everything in order.