It's not that widely used (although it should be) but it is possible to use Feedburner to email subscribers (opt-in) with a daily summary of your blog posts. If you want email updates of this blog then subscribe here.
Today (at least for feeds I get by email) Google's ramped up the presence of the RSS subscription option. The top of the daily email now carries a #+Google# RSS subscription badge.
The footer of the email has recieved similar treatment. Among the unsubscribe options (which includes writing a snailmail letter to Google) there's another #+Google# button.
I'm actually quite glad for this. If the reader is considering that their inbox is too full then I'd rather they move to RSS than unsubscribe completely.
Feedburner's Email service remains an odd child in Google's family.