I tried Opera on the iPhone last night...seriously disappointing. I used to love Opera on my little Blackberry Pearl, but it's soooo slow on the iPhone. Interface is odd also.
I had the same experience with their Android version. Tried it, but I don't see a reason to use it over the default browser (and yeah, the interface is a little odd).
It's perfect if you find yourself having to access an heavy site on a low bandwidth (or just spotty) connection. Using it on WiFi is pretty pointless.