I've been hearing this back from a lot of my subscribers (I run weekly JavaScript, Ruby, and HTML5 newsletters). They've gotten sick of the deluge that accompanies RSS feeds and the lack of discrimination that sometimes occurs on Twitter and they trust me to curate that info for them. Of course, the next step is to expand into some slightly bigger niches ;-)
Of course, there's the "why aren't you doing this with RSS" crowd too, but with 25k subscribers and growing, I'm finding it pays to focus on those who actually want the e-mails!