If you mail me at jgc.org your mail is routed to a GMail account and then some magic happens. Your mail will be read by my automatic mail classifying code and automatically labeled. Here's a shot of my GMail labels:
All those labels with a + as a prefix are automatic. Here's what happens: every five minutes a service I've created logs into my GMail account using IMAP and OAuth (the service doesn't know my password, it's authorized via OAuth to access my mail). The service searches for labels with a + prefix and synchronizes.
Then it looks for new messages in my Inbox (and All Mail) and uses machine learning to apply one of the + labels to the message. Next it takes a look through the labels themselves to see if new messages have been labeled manually. It does that so it can learn.
When first set up the service looked through all the messages in the + labels and built a machine learning classifier from the message contents. It immediately after that started classifying mail. But, naturally, it's not 100% perfect and so sometimes it makes mistakes (puts the wrong label on messages). Happily, all I have to do is change the label in GMail and the service will spot the change next time it logs in and will update its classifier.
The entire interface to the automatic classifier is through GMail. In fact, there's no interface at all: it watches my actions and learns. All I have to do is set up labels with a + at the beginning and my mail is magically labeled. If an labeling error occurs I just relabel.
Anyone else OCD enough to want this service? (If you are serious about wanting a service like this please email me and I'll add you to a little mailing list for when I get round to implementing it for public consumption).