Why do I need to "sign up for the beta"? Why do people think this is the cool trendy thing to do? Let us have it or let us know when it's finished. I don't need to know about it now.
Are they fishing for a buyer?
Yes, plus I don't feel there is enough info on the website. Just a high level overview and not enough nitty-gritty.
Its the same reason why bouncers out the front of clubs only lets certain folks in. It creates exclusivity, regardless of whether it is warranted or not. For me, it is a crappy.
Does it work with Enigmail? (OpenPGP...)
For me, GPG is an integral part of working with email.
I've been using the alpha of Polymail for a few days now, it definitely exists/works and is actually pretty awesome.
How can it tell when my mail has been read?
I am sure you will use their server(s) somehow ("added value service"). Yet another email client that is more than what it seems. Of course, all speculation.