This how you can display the most recent blog posts from a specific blog or blog group on your Community Server home page.

Open up the default.aspx file in the root (home page) and in this section just add the desired blog (SectionID="") or group (GroupID="")

In this example I am using a specific group also notice the PageSize="4" this is to limit how many posts show at once on the home page.

To determine what the ID value is for a blog or a blog group just go to the CS Control Panel > Administration > Blogs and to either Blogs or Blog Groups in the Grid View just hover the mouse over the group or blog and look at the bottom of the browser for the ID in the status bar. 

<Blog:AggregatePostList runat="Server" PageSize="4" id="AggregateBlogPosts" EnablePaging="false" EnableTitle="false" GroupID="7">
                    <SkinTemplate>
                        <h2 class="CommonTitle">
                            <asp:Literal runat="server" id="title" />
                        </h2>
                        <Blog:AggregateList id="Posts" runat="Server" EnableTitle="false"/>
                    </SkinTemplate>
                </Blog:AggregatePostList>

I have also done an article on adding back the front page news to your Community Server2.1 sites here.