Mmmmm. I don't really agree with Gerri that fear of Facebook or ignorance of how the site works was a motivator for my cautionary post.
I too am a Facebook user and consider myself a fairly high-end digital consumer.
But I would urge the people setting up this group to very carefully consider the possibility of the future potential risk with regards to health insurance access and employment discrimination that the members of a HER2 group would be accepting and complicit in encouraging.
For the sake of debate - how about looking at other types of social networking that are less exposed to commercial exploitation?
One possibility which might appeal to you that could be used in conjunction with this current site is a downloadable tool which gives users the ability to "see" each other in real time when they are simultaneously surfing any website & converse with each other. An example of which is here
http://www.rocketon.com/a/index.php. (I haven't researched this example - but there are other analogous choices out there)
Another possibility would be a group membership at Second Life. This is one of the biggest, fastest-growing avatar based virtual reality worlds on the internet. Universities offering classes, banks, law firms and Reuters news wire all have virtual bases in this world. A base can be set up so that membership can be either "open" or "invitation only"
http://secondlife.com/whatis/
Another possibility is Twitter - I think Tweets can be anonymized more effectively than Facebook membership.