Gmail gets auto-replies
Useful new feature if you deal with a lot of the same message.
This is probably more useful than GMail's last goofy new experimental feature (Mail Goggles): Canned responses (see Official Gmail blog). You can now save a reply you're writing as a "canned response" and then quickly select one of these responses when you're replying to a future e-mail.
You can also have your Gmail filters auto-reply to messages for you with these reponses. I quickly set up a filter, for example, to reply to people who send me an e-mail with "pitch" in the subject line with a message asking them to reach me on my work account.
The canned response feature is useful and nicely done. If you often have to send people the same (or close to same) e-mail, you'll find it useful. The auto-reply filter is a bit more complex and potentially dangerous, although it is useful. To set up an auto-reply, you have to first save the response as you're replying to an email, and you have to make very sure that your filters aren't going to get you in to trouble by sending out your message to the wrong people. Fortunately, Gmail lets you pre-run your filter on your exisitng inbox to show who which messages would be swept up in your filter if it was already running.
If you use Gmail to handle work-related e-mail with a lot of typical queries, it's worth trying.
To turn on the Canned Responses feature go to Settings | Labs. To use the auto-reply feature go to Settings | Features.