I'd prefer receiving tweets from twitter about completing skills, etc. rather than via email. The APIs exist for integration, via explicit permission of the user.
I don't want any notifications. I'm actually kind of miffed looking at my inbox now. Do I need to know what I completed while I'm in-world? Nope. An email diary telling what I completed while gone from the world would be one thing or even a weekly log...no, even a weekly log would annoy me.
If you click on 'Account' up in the top right, then 'Update your preferences' down near the bottom of the new page, you can choose exactly which email updates you receive, including disabling them completely.