I think its good idea to have a more control of what e-mails send by shop looks like. I mean we live in XXI Cent 
and plain text isnt enough anymore. I would like to see some type of editor (like visual HTML editor) to see what my email will looks like and not to have test it by creating test acc just to see how emails will look at the end.My english isnt that good enogh to tell ya all what i mean but maybe someone will “oversize” my idea.
The cart emails are html not plaintext and you can edit the .tpl files in a popular website editting program
check out
…/skins/default_blue/mail/orders/invoice.tpl