In good light, it actually performs very well.
Parthenon
Or even in mixed lighting, as long as you know how meters work.
Bridge of Sighs
Forget the useless flash in backlit situations, but the AE lock feature helps:
Back of the Bus, Dubrovnik
And I don't think you can beat it for stealth:
Sketching the Colosseum
Or getting off a shot quickly
Kotor, Montenegro
I really liked the easy-to-use panorama for sweeping scenics
Venice, Italy
Santorini, Greece
Dubrovnik, Croatia
Or to play around with.
St. Peter's Square
And even to convey space in crowded street scenes.
Piazza Navona
Just be careful with subject movement, like when Miguel decided to skip a stone while I was panning.
Kotor, Montenegro
There are, of course, other limitations. A big one is that "zooming" is basically cropping, and will quickly deteriorate your photo. Just try to be judicious and use only as little of it as necessary.
This view of St. Mark's from the cruise ship shows a lot of noise particularly in the sky, but I otherwise would not have been able to capture it.
All in all, as long as you stick to the same sound basic techniques that you would use with any camera, I would think that the iphone is capable of decent results. And along with the numerous advantages, especially the portability and unobtrusiveness, I can see why many tourists are happily snapping away with their smartphones. Sometimes, it may even surprise you, as with this dreamy photo from a cliffside cafe in Santorini
What I don't get are the folks taking pictures with ipads.....