Now when you use the Gmail mobile web app, you�ll have a small window of opportunity to undo four key actions: archive, delete, add or remove a label, or move a message/conversation.
When you take one of these actions, Gmail displays a yellow bar that recaps what you just did and allows you to undo it:
This bar stays in position even if you move to another screen (e.g. moving to �Menu� from �Inbox�). If you don�t happen to catch your mistake in time, not to worry: all four actions can still be undone through other means (e.g. you can move a message from Trash back into your Inbox).
Try it out at gmail.com in the browser of your Android or iOS device.
Update: 9:09am Pacific time 4/19/11 - This update is available for phones running Android or iOS, but not tablet devices with the two-pane Gmail UI. It is also now available for BlackBerry OS 6.0 phones.