Yes, you can print them. Quality depends partly on the phone (e.g., 5 has a better camera than 4), and partly on you (e.g., can you hold the phone steady, not cover the lens with your finger, use decent lighting, etc.). The front-facing camera is not as good as the rear. There are a ton of great apps to help take photos - my latest favorite is Burst Mode, I got some great fireworks pics with it. And a ton of great apps to easily edit photos.
Photojojo has a decent and simple iphoneography course.
I've blown up iphone 5 pics to 12x12 size and they look fantastic.
I don't like the iphone HDR very much. There's a great app called Pro HDR, I adore it for landscapes and 'still life' type images, but it's not great for people pics as it takes two pictures over several seconds, it's hard for people to stand still enough that long.
Oooh - and my most favorite thing is the Olloclip! It's a lens attachment that can do wide angle, fisheye, and macro. They have a new telephoto one, too. Great quality lenses. DH and I go to the local conservatory of flowers a lot, we always take pictures, and people ALWAYS ask us about the Olloclip.
Photojojo has a bunch of fun phoneography equipment (I should get kickbacks, lol).
Just today I plugged my iphone in to my computer, then went to My Computer and under devices there was my phone. A few clicks allowed me to download all the pics to a folder. From there you can edit them, burn to a disc and take to print or use online services as you would normally.
I took pics a few weeks at the zoo with my phone as my camera battery was dying and was shocked at how good they came out. I thot they'd be crappy but they were crisp.
Do you love them? Are they one of a kind photos? Then use them!!! Don't miss out on scrapping a person or event just because you wonder if your photo is "good enough". You could, of course, check to see if anyone else got a better photo that you could use, but don't let this stop you from the joy of scrapping.