There is an option is almost all cell phones to send pre-written text messages, often stored under a section "Templates". That's a very useful feature since typing the same message can be tiresome particularly on a small keypad. Now the same feature is brought to Gmail with a new Labs addition called Canned Responses. When you enable this feature, every time you have to reply to someone or compose a new message you will see a new item "Canned Responses" under the subject box.
Write your common reply to that boring common question and click on Canned Responses to save it. In future when you have to send this same message, all you have to do is select this pre-made response from a drop down list and send it. Saves time.
Canned Responses is also available in the Filter section as one of the actions to perform on a filtered mail. If you have properly setup a filter based on your incoming messages, it's possible to setup a different automated reply for different queries. Awesome!