When I get emails, I expect them to be from either friends or from clients. I like my friends enough to want to see the things they send to me ASAP; I want to hear immediately from clients so that I can respond to them at four in the morning (if I'm up anyway, that is). Know who I don't want interrupting my workflow? You.
If you're looking to get my attention because you've got a new feature or you generally just want me to come back to you, then come up with a way to make me want your reminder. Have me become a fan of you on Facebook, so that you can push to my feed. Have me follow you on Twitter. Publish your story to Hacker News, and make sure it's good enough that I'll notice it and check it out again. Get a blog and push your updates to me through RSS. But when you email me, you're being a jackass.