I have been seeing this on and off, recently.
When I am searching, and get forum links, as search results, On some of them, I can see the number of posts and the day of last posting.
Surprisingly, this is not happening on all results, on a page, even if they are from one site.

http://i308.photobucket.com/albums/kk348/dev3_44/google.jpg

Discussed here:
http://blogoscoped.com/forum/142613.html

[Moved from "When searching forum posts Google will show are the posts fresh" – Tony]

Just a short note that Google now shows more(?) information when search results are from forum sites:
i.e. '2 posts – 2 authors – Last post: 20 Sep'

Is the Last post information now?

When the related Blogoscoped forum thread is known the the Last post information is not new (there was a typo – new, not now)