Gmail Labs (Please note labs features may not be permanent and may give you trouble, but if so happens you can escape lab monster by going to http://mail.google.com/mail/?labs=0 and Labs will be temporarily disabled.) Has introduced "Canned Responses" Gmail.
This should come in handy if you have to send a reply(ies) to without having to type same thing 20 times, in cases like responding to your blog visitors.
If the feature sticks, I think it will be nice to use this as a custom signature. You can have multiple signatures based on blogs, business and personal etc. Perhaps Gmail should rerelease this as Custom Signature!
You can try it by visiting Gmail Labs