Yes, usually something like this (I just got this last night for the Ubuntu site):
Hey everyone!
The Ubuntu Stack Exchange site, for
Ubuntu users and developers, is now in
private beta.
Since you committed to the site, we’ve
granted you access at:
http://ubuntu.stackexchange.com
Please help us fill up the site with
awesome questions and answers so that
when we open to the public, the site
will be stocked and ready to go. The
questions on the home page when we
launch to the public will set the tone
and topic of the site for a long time,
so make them great!
FAQ
Q: Why am I getting this email? A:
Because you committed to support this
new site on Area 51.
Q: Who can access the site during the
private beta? A: Only the 594 people
who committed to it.
Q: How do I log in? A: Use the same
Open ID you use for other Stack
Exchange sites. You will be creating a
new account on
ubuntu.stackexchange.com, but it will
be automatically associated with your
account on other sites from the
network.
Q: When will the private beta end? A:
The private beta will end and the site
will be opened to the public in
exactly one week, at 7 PM UTC on
Wednesday, August 4.
Q: How can I help the site succeed? A:
During the private beta, ask
questions, answer questions, tag
questions, edit questions, and vote.
Q: What else? A: The minute the public
beta opens on August 4, invite your
friends. Spread the word via Twitter,
blogs, and email far and wide. Hang
out on the site answering incoming
questions during the first few hours
so that newcomers understand what a
great experience a working, popular
Stack Exchange site can be.
Remember – the private beta is now
open, but the public beta will open on
Wednesday, August 4: US Pacific - 12
PM US Eastern - 3 PM UTC - 7 PM London
- 8 PM Sydney - 5 AM Thursday
Q: Where do we talk about the site? A:
We don’t want to talk about the site
on the site itself, so we set up
http://meta.ubuntu.stackexchange.com
as a place to talk about things like
what questions are appropriate, what
tags we should use, etc.
Q: How long is the beta? A: The beta
will last at least 60 days. At the end
of 60 to 90 days, if the site has
enough ongoing traffic and enough
questions are getting answers, it will
graduate to a full-fledged, permanent
Stack Exchange. At that time the
community will decide on a permanent,
top-level URL, a web design and a
logo.
Q: What else? A: Nothing! Go to it!
Here’s the URL again:
http://ubuntu.stackexchange.com
Yours,
The Stack Exchange Team
Then you get another one when the site goes into public beta, but much shorter.
If you aren't receiving them, check your SPAM folder. If its still not there, try using / verifying another e-mail with Area 51. Services like Hotmail are notoriously paranoid when it comes to that, and its conceivable that several people who committed use the same mail service that you do.