Whether or not you like Opera Mini (using the Mini 5 Beta on my G1), at least you now have a choice. Pretty soon you might see Firefox or Chrome, if Mozilla and Google are so inclined to port their browsers.
Fact of the matter is, lots of people like Opera (and Opera Mobile, and Opera Mini). Now that it's an option for iPhone users, its a good thing. Just because you don't use it (or anything else Steve Jobs didn't personally crap-out), doesn't mean its worthless.
And no, if you're on WiFi or 3G you won't notice much of a speed difference, but if you are in the other 80% of AT&T coverage area that doesn't get 3G (remember those Verizon commercials), you WILL appreciate Opera's server-side rendering. It makes it much faster than locally downloading and rendering everything on the page. I especially like the image compression, which reduces the quality (if you tell it to), and also scales the image to fit on the screen. That saves lots of unnecessary data from being downloaded.