Hello, you've reached Chad's mailbox. Thanks for your email about the latest Labs feature: Canned Responses, or email for the truly lazy. I'm on paternity leave so I won't be able to respond personally. Instead, I hope you'll enjoy this automated message.
If you're sick of typing out the same reply every time someone emails you with a common question, now you can compose your reply once and save the message text with the "Canned responses" button. Later, you can open that same message and send it again and again.
It couldn't get any easier unless Gmail automatically pushed the Send button. If you're lazy enough to think that would be a good idea, then read on, friend.
Gmail already lets you create filters based on a combination of keywords, sender, recipients, and more in your incoming messages. Turn on Canned Responses in Labs, and you can set a filter to grab one of your saved responses, create an automated reply, and hit the Send button for you.
You can set up different automated messages for different keywords, just like you said you wanted. (We're friends, so I trust you to use this power responsibly.)