Well, suffice it to say that people have a variety of opinions on this. I bought an iPhone (mainly due to some work-related reasons).
Safari, and the lack of an Opera option, were the main reason I really wanted to go with a Blackberry and NOT buy the iPhone. IMHO, Safari is great for making iPhone commercials that look cool, but in terms of usability, it has some serious problems, mainly that you cannot change the size of the text, independent of the layout. So, if I zoom in to make the text readable, then I have to constantly scroll right, and then left, and then right, and then left, and then right, and so on. Opera handles this much more gracefully, albeit with less glamour. Another problem with Safari on iPhone is that it crashes every few minutes. It is extremely unstable. Furthermore, Safari on iPhone doesn't let me sync my bookmarks and other things that would be awfully nice to have on iPhone.
I'm happy if you (and others) enjoy Safari and don't think these shortcomings are important to you, but personally I'd love to have some viable option, preferably Opera.