Chris Mills on Mobile Web Development
Opera’s Chris Mills writes a great article titled Coding for the mobile web which I heavily recommend for any of you who is interested in developing websites targeting mobile devices, or just any webdesigner/webdeveloper in general, because you should make sure your website runs on mobile devices too.
In this article I learned something that I find amazing I didn’t know before: the fact that some mobile browsers, like Opera Mini in this case, work through a proxy system. This is, when you navigate to alcidesfonseca.com, you’re going for a opera script that fetches this website and formats it in a way it fits perfectly your browser (and saves you bandwidth costs!). I must say I’m admired! From the use I gave to Opera Mini, the speed didn’t make me think there was an external proxy doing this!

André Luís
If you're really interested in the dos and don'ts and also the why's of the mobile web, I strongly recommend Cameron Moll's book. Chris links to it in the article.
Oh as for Opera Mini, it's worked like that ever since the first release. Pretty handy if you're accessing over the GPRS. I still think it uses the proxy regardless if you're accessing via Wi-fi, which sometimes can be a bit annoying.