OK Max if you really must....
http://www.washington.edu/computing/...129/other.html
I belive the bit about stationary will tell you what you need to know.
I think the point we are all making is that you message is probably more important than your logo to most people who will get mail from you and by adding your logo the email will either take longer to download due to embedded graphics or longer to display while images are retrieved form the web - assuming the reader is still online.
How the mail dislays will also be unpredicatbale as not all email programmes allow the display of this type of message for security reasons - some people may get you message as pure HTML code.