Providing a way to subscribe to a blog via email is important. Many, and perhaps most people don't understand RSS, atom, XML nor would they know how to set up a reader. Heck, I hardly understand this stuff. These folks have no way of knowing about any new posts unless they frequent the blog.
I have been contemplating rolling an email subscription module for dasBlog (and other blogging engines). Then I started investigating further. There are several such services available all of which have their pros/cons. Some are: AWeber, Zookoda and FeedBlitz.
First, I didn't look into AWeber after seeing that the starting price was $19.95/mo. I'm looking for a free option so it wasn't worth my time to dig deeper. 
FeedBlitz seems to be the front runner in terms of reliability (see this review). it has a free version that places ads in the resulting emails. The relatively inexpensive paid version will remove the ads and I believe will provide some additional functionality. It seems feature rich, and the account setup was easy. Once setup, you have tons of options for managing newsletters (specifying RSS feeds for bloggers, scheduling distribution, look and feel, etc). I have not looked into monetizing the emails but FeedBlitz appears to support it. There are two ways to incorporate it into your blog. One is to use the supplied Form based html code. The other is a link that will take the user to a FeedBlitz hosted subscription form. Obviously, the form based code will not work with dasBlog :(. Overall, I really like this service.
Zookoda was very user-friendly and has a fairly nice feature set. After setup, it takes a day or so to receive a Sender account with which you can start sending emails. Basically, you setup your mailing lists, emails and broadcasts and specify how they are to be distributed. I particularly like that mailing list management aspect of this service. Also, incorporating it into your blog uses javascript and so you can have the email entry right in your site if you use a blogging engine like dasBlog. There are problems with this service however. Based on the review above, its not very reliable in that many subscribers never receive the broadcasts.
Furthermore, the company is owned by PayPerPost. There appears to be some controversy around this company regarding their advertising model. I prefer to stay away from controversy.
Currently, I'm using FeedBurner which also provides an email broadcast service. It is more than sufficient. Like FeedBlitz, it uses a form based script so incorporating the form into a dasBlog site is not doable. However, it also provides a subscription link that will take the user to a different screen. One thing I'm not sure about (I'll have to look into this) is whether FeedBurner will allow you to put a character limit on each post that get sent out in email (both FeedBlitz and Zookoda do). This is important if you are trying to drive traffic to your site if you are monetzing with ads and such.
I may provide FeedBlitz as another option for my site. Comments on other options/suggestions are welcome.
----
UPDATE Apr 28,2008: Looks like FeedBurner does not allow for a character limit on the emails sent. So subscribers will get the full post in thier emails.