Results from Google Groups are now visible (query dependent, of course) in a OneBox on Google web results pages. The addition is documented on the Google Web Search Features page. Unlike other OneBox results that embed relevant links from Google Local, Google Print, Froogle and other sources at the TOP of web results pages, the OneBox for Google Groups appears at the BOTTOM of web results pages. Here's an example. The Google Groups OneBox contains three direct links specific posts along with direct link to run the query in the Google Groups database. These results are also set apart with two icons. The first a balloon with a question mark inside. The other a balloon with an exclamation point inside.
Postscript From Danny: We'd seen Google experiment with bringing this in at the end of August, but I can't recall if it was documented then. I don't think that was the case, but it could have been.