Google has announced a new Gmail engine for iPhone and Android users, adding features like (some) offline access, a "floaty bar" for archive, delete, and more, and quicker access to search and tasks.
The new interface also now displays email labels, and everything should run quicker and smoother in general. iPhone (and iPod touch) users will need to be running the latest 2.2.1 operating system for access to the latest and greatest features and interface. The new and improved Gmail for mobile is rolling out over the course of the day, and it works for both regular Gmail and Google Apps accounts.
Gmail gets a new engine for iPhone and Android-powered devices [Official Google Mobile Blog]