If you have an iPhone 4S or 5, I'd say yes. The camera on the newer iPhone is really good. And as the cliche goes, the best camera is the one that is on you. The reasons to use a "real" camera instead of the iPhone would be:
- better low light performance -- so that you can take pictures without flash indoor, in the evenings. The Cannon S90 and up can do that
- lower shutter lack -- you can start taking the first picture quickly, and can continue to shoot instead of waiting for the camera to recover -- Really only DSLR can do this well
I own both the S90 which I pretty much stopped using. I own a high end DSLR, Nikon D7000 which I use when I need to take pictures at kids sports events indoor and out, or when I am actually planning to do some photo shooting sessions. Otherwise it is the iPhone!
Meanwhile, here are some pictures taken with my iPhone 4S:
iPhone as Family Camera, a set on Flickr.