The iPhone 3G's Safari browser works surprisingly well for a mobile phone browser. It's not as full featured as the one on your PC right now, to be sure, but it's astonishingly close. It's undoubtedly a mile ahead of anything that anyone's put on a phone to date, both in terms of the way it renders web pages, and the way you can zoom between them, run multiple pages and even rotate the screen display to make some pages easier to view.
Safari supports secure HTTPS sessions, meaning it should support online banking (although we'd strongly suggest not doing so from a public Wi-Fi hotspot), but one thing it doesn't support yet is Flash-based websites, including YouTube. Yes, there's a YouTube link directly on the iPhone 3G interface, but that's due to wheeling and dealing between Apple and Google (owners of YouTube) that sees 'selected' YouTube content re-encoded in an iPhone 3G-friendly .H264 video format.
Internet use (along with email) will form a major part of most people's data usage, and with many web pages these days weighing in at the multiple megabyte level, for things like banking and online ticket ordering, combined with the somewhat expensive data plans on offer for the iPhone, it may well be worth using the phone's calling capabilities for some tasks that can be done quickly, rather than the web interface.
