Apple Thoughts: iPhone 4S Video Versus Canon 5D MKII Video

"The iPhone 4 already offered standout image quality for a mobile phone, helping to further the general trend of using a phone camera rather than a dedicated camera. And with ever-better video, phone cameras will increasingly will be able to supplant videocameras, too."

I don't think we are there yet, but the iPhone 4S camera is pretty darn good, and for day to day stuff it's totally passable for your video needs. This is one of the reasons I'm strongly considering switching, as I have some events coming up that I need to film but don't necessarily want to carry around several devices. Like they say, the best camera is always the one you have with you.