Stephen Shankland at CNN has a good review of Google's new Gmail application for mobile phones, particularly the iPhone and phones using Google's Android platform.
The new Gmail app allows users to access messages while offline, and even to compose a message without an internet connection. Gmail automatically takes care of sending the message when the connection is restored. The new app also allows users to select and modify, move or delete multiple messages at a time. There's also a menu that appears wherever the user happens to be on the page, removing the need to navigate back to the top in order to do anything.
The search button now appears at the top of the page, whereas in previous versions it was virtually invisible at the bottom of the inbox. This always seemed like a major oversight from Google, the search engine mega-giant, but at least it's been addressed now.
While I can't speak to Android users, the Gmail app is much more usable and feature-rich than the native iPhone email application. The one advantage that the iPhone email has is its ability to give an alert when a new email arrives, but if you're an obsessive email watcher, it shouldn't matter too much.
Shankland points out that, beyond the app's impressive functionality, perhaps its most important aspect is its demonstration of the power of the mobile web application. Companies are starting to develop meaty programs for use in a mobile browser, avoiding the necessity of creating different stand-alone applications for each smartphone application.