If you're lucky enough to have a Google Wave account, you may be familiar with Waveboard. I started out using Wave via a Fluid SSB, running Wave Growl for Growl notifications and Dock badges. Then I found Waveboard, and it made things smooth enough that I haven't looked at Wave any other way since. So, obviously, I'd been anticipating the iPhone version of Waveboard. It's here, and it's, well, moderately interesting.
The desktop app is essentially a Single Site Browser, like a Fluid app, but it adds handy, Mac-like keyboard shortcuts, Growl notifications, Dock and Menubar notifications, etc. The iPhone app is the same, a webkit browser showing what Google already provides, but there just wasn't as much potential integration to take advantage of on the iPhone. They took advantage of the shake gesture to reload or log out. Websites can be opened in the same browser or sent to Safari. Landscape mode is supported. And you can kind of get push notifications, by using Prowl (which Aron has mentioned before). Setup instructions are available on the Waveboard blog.
That's about it, for now. Google hasn't offered an API, which seriously hampers a developer's ability to do cool things. More features are reportedly in the works, so we'll see if it turns into a truly useful counterpart to its desktop cousin over time.
Waveboard for iPhone is available on the App Store iTunes link for $0.99US. Under a buck, and it might be worth a look for avid Wavers (which I would be, if enough of my clients and cohorts had accounts to make it truly useful).