Hans Hugli, a friend of mine (we worked together on Microsoft's evangelism team during the heady dot-com days) and developer on Microsoft's UberDemo team wrote up a great article on SharePoint and Community Server integration. Below is an excerpt:
The business scenario discussed in this article is how to enable Community Server site users to log on to sites that are running Microsoft SharePoint Products and Technologies, by using the same credentials they use to log on to their Community Server site. Much of this article is based on Steve Peschka's post on the official Microsoft SharePoint Products and Technologies blog. I recommend reading through his blog to get a better understanding of how this works by using SharePoint Products and Technologies. The blog entry describes how to integrate the membership database of Community Server with the security model used in SharePoint Products and Technologies. This article assumes a limited knowledge of Community Server, SharePoint Products and Technologies, and Microsoft ASP.NET.
You can get the complete article here.
If you are a SharePoint & Community Server customer let me know, I'd actually love to chat with you about some of our plans to integrate the two.
We're also looking to hire a developer who knows SharePoint (or wants to learn) to set the foundation for our SharePoint and Community Server integration plans.