I did this a lot when starting Hacker Newsletter (http://hackernewsletter.com http://hackernewsletter.com) and it seemed to always have a positive response and

I did this a lot when starting Hacker Newsletter (http://hackernewsletter.com http://hackernewsletter.com) and it seemed to always have a positive response and in a couple cases lead to more (like twitter mentions, reviews, etc.). If you want to do this, your friend is Rapportive, as it can quickly give you a starting point when tailoring your email and/or help you decide who to email.