I came across this plugin today and from what I've seen so far, it looks absolutely gorgeous. I just can't use it because it's missing too many features. I'm currently using the ALO Easymail plugin which has some good (not great) features which I don't see here and is missing some your features.
1) Bulk import (unless I'm missing this somewhere). The widget signup is great, but I do networks of sites for a large non-profit organization which already has it's own mailing list. I need to be able to import the existing lists and assign the recipients to one or more lists.
2) The ability to use a post as an email subject and include an excerpt in the body. ALO currently allows this. I used to use the old Bloghoster program (www.bloghoster.net) and they took that one step further with a feature that my users loved. In Bloghoster before they published, they could click a Yes/No box that said "Send to mailing list" and an email with a predetermined text template would go out to their entire mailing list as soon as they published. That was awesome integration and a huge traffic generator. (See attached screenshots)
3) I'll echo the comment from the other thread which said that each site in a multisite installation needs to have their own mailing lists. There's no way on God's green Earth I would want my subsite users to have access to my master mailing lists.
4) ALO recently went to a system where their newsletters get published to the website as well so those who have trouble reading the emails can read them online. (This isn't crucial for me, but it is a nice feature.
5) Would also like to see some documentation on the available shortcodes for templates. The templates you have are nice, but I'm sure my customer would want a custom template.
All that being said, it looks like you're off to a great start and I'm looking forward to leaving ALO behind.