Apple release free MobileMe Gallery iPhone app
With the application, you can view your own gallery (including password protected areas) but also view movies and photos that have been published by your friends. The app also remembers the photos you've looked at and will let you continue to do so even if you're offline.
In my brief testing, the application was great! It was really quick to load photos and video on both Wi-Fi and 3G, and the ability to email links and view photos offline is really convenient.
Just a side note, even if you just want to view friend's photos you'll still need an active MobileMe subscription.
Here are a few shots of the application in action: