I usually never sign up for these pre-releases, but after I read through the intro, I "signed up for the beta" expecting to actually see some of the app that was described as so amazing. Instead I am now subscribed to a mailing list.
I just don't think that is cool. At the very least you disclose this before I gave you my email.
Of course, I'm happy to remove you (and anyone who signed up by accident) from the mailing list - send me an email to ben at zeninbox dot com :)
The point I was trying to make (rather poorly as usual), is that the reward for the email address is misleading. I was expecting access to a beta product, not an automated email from MailChimp that told me I was now subscribed to a newsletter.
You response here is classy, and I have no problem -- but I think you ought to change the wording to be "sign up for our newsletter and be alerted when you can participate in the beta".
Good luck and I'll try to remember to check back.