We're big believers in evolutionary design rather than revolutionary design. With milestones, this became especially true. I briefly shared our thinking behind designing and building milestones into Sifter, and this is a follow up to show how our thinking and the interface have evolved.
http://nextupdate.com/blog/archives/2009/05/milestone-improvements/We'll only send emails for significant product announcements, and those happen every couple of months at most. Of course, we won't give away or sell your e-mail address either.