Thanks for your interest in MultiBit HD.
We are coordinating the testing/ announcements using a Google group here:
http://groups.google.co.uk/d/forum/multibit-hd-private-betaThere's an anti-spam approval step but I'll keep an eye on it for if you sign up.
MBHD is in beta but it is pretty stable now. I've been doing bug fixes for the last few weeks and it's things like:
"When you paste a password rather than typing the next button does not enable". Stuff like that.
There is still a fair amount of finishing off to do e.g. localisation, help files. The website refresh is more or less done now.
Also, the bitcoinj library we are using (which gives us the HD wallet functionality) is still "0.12-SNAPSHOT" which means that that is still technically in beta.
If you are interested in MBHD then testing of the functionality is very useful to us.
Don't use it with more than 'a cup of coffee and a donut' worth of BTC though.