Last week I sent out our annual Christmas letter, mostly by email, with pictures embedded in the text. I used a mailing-list program that comes standard with my Web hosting account. Judging from the responses I got back, people liked getting the letter by email (in part because they could respond conveniently), and my wife and I certainly appreciated not having to fuss with photocopying, addressing envelopes, etc.
The drawback was that I couldn't add individual messages. And that gave me a feature idea for the services like LinkedIn, Plaxo, and Facebook: Let users send out an email newsletter to contacts they specify, but also let them include an optional individual message to each recipient in addition to the standard letter.
For about three seconds I thought of building such a feature myself and selling access to it. I know I could figure out how to program it, using existing open-source software. And as a user I'd pay $20 or $30 per year in a heartbeat to avoid having to buy cards, envelopes, and stamps, not to mention the time savings.
But even at $30 per year, it'd take a lot of users to make any real money.
And any of the existing services could overwhelm my efforts in an afternoon.
So I'm hoping that next Christmas, one of the existing services will get the idea and offer this feature themselves.