Jane_Doe - 2:20 am on Dec 12, 2006 (gmt 0) For some reason, that really sets people off. :)
While the safest and most mature course I think is to ignore people like that, if you do want to get a reaction, you can always send a return form letter pretending you didn't understand his email, and thank him for expressing an interest in your site. Then add that due to time constraints and the volume of mail you receive from your site due to its high rankings, you are unable to provide a personal reply.
For some reason, that really sets people off. :)