Here’s a thought (I had in the middle of a dream about brightly garbed superheroes): use Personas to style email messages in Thunderbird! It’d be a simple way to easily add some style to your messages to friends and family, highlighting your current mood, your perennial interests, or the subject of the message.
There are some tricky issues, like how to select a background color for the message that blends in attractively with the bottom of the header image. And it’s not clear if the footer image is useful in this case.
But overall the idea seems quite promising. What do you think? And, if you’re a Mozilla extension hacker (or would like to become one), would you be interested in prototyping it?