One of the consequences of the huge spread and success of the iPhone is that a lot of popular Websites have started implementing a mobile interface, so that it’s better displayed on portable devices with smaller screens, and most of these scaled-down versions are rendered beautifully in iPhone’s MobileSafari. Not only that, they retain all their major features and are more accessible at the same time.
A very nice side effect is that mobile versions can be quite useful if you’re using a vintage Mac with a vintage browser. They usually load faster (especially Gmail), render better, and are overall more compatible with the limited capabilities of older browsers. What’s more, they’re usable: from my PowerBook 5300 with Mac OS 8.1 and iCab 2.99 I can tweet, read and write email using Gmail, enjoy a decent experience in Flickr, and so on. See some examples below: