Google has just released version 2.0 of Gmail's mobile application for Java-enabled phones. Now it supports offline mode and switching between different Google Mail accounts (including Google Apps Mail).
Composing an email offline makes the application more useful. Email file attachment is one more missing feature to complete Gmail for the mobile platform. And I still waiting for the offline Gmail on my desktop browser. Come on Google, you are almost there.
(screenshort from a Nokia E61i)