Opera mini can't render those Android and iPhone optimized pages with collapsible sections, smooth pull down menus and the suggestions on Googles home page. I think it might be Webkit thing.
Hell even Walmart's mobile site has a version iPhone and Android
I'm all set. Not knocking opera, they saved the web browsing for WinMo and feature phones. I also like having a choice. But people might miss out on how awesome the Android browser is if they use opera. I know it's a beta but all the versions of opera can't do this. Not to mention it takes a few more seconds to load. Opera should innovate and not set browsing back.