Here's a service idea that came up the other day on Hacker News: automatically labeling your mail in Google Mail.
I have quite a lot of experience in this area having created POPFile for this purpose and then sold a commercial version called polymail.
But with the rise of Google Mail, and with the safety of OAuth, I'm wondering whether there are people out there who'd pay some small amount of money per month to have their Google Mail automatically labeled.
The service would work like this: you'd sign up and give me OAuth access to your Google Mail. Within Google Mail you'd label mail as you see fit, but in the background service X would be watching and learning. As new mail arrived it would automatically label your Google Mail based on what it had learnt (imagine waking up to a mailbox full of pre-labeled mail).
If it made a mistake you would simply change the label on a message and service X would update its machine learnt view of your labeling habits.
So, would you use this? How much is this worth to you?