Orchard 1 sites on DotNest use a smarter template for body summary. This enables the following when you publish content items that use the Body part for storing text:

• Content items displayed in summary (e.g. when listing them) will show the first paragraph of the text body.
• If you add the <!--more--> piece of code to the HTML of the body (by editing the HTML through selecting "Edit HTML Source" in the editor: look for the button that says "HTML") then that will handle were to break the content: everything before it will be shown in the summary and everything after it will be only shown when opening the content item in detail.