Sgt, i don't even want to call them as mashups as they aren't. A mashup is a site that aggregates some good related content (text, videos, maps, photos, etc.) and presents them in a form that is loved by the users. However, I do want them to do it only if they are allowed to aggregate such content by their original owners. otherwise, it is copyright violation in my opinion.
But i have seen several sites that mashup content from google platforms being dumped on their SERPS in the last 1-2 years.
Google+ will only have 1 or 2 lines of text and a thumbnail from the shared page. Unless the user comments on those pages are of real high quality which I doubt, this is a very poor echo of the original copy.Ranking them high because it is on a google platform and hence automatically qualifies to be an authoritative site, is manipulation.
There were several such echoing sites ike digg, stumbleupon, etc which are almost dead on the SERPS, despite being in existence for so many years. But I don't want them to be on the SERPS as they aren't the original sources.
Though the google mouthpieces claim they like only original and unique content on their SERPS, they are choosing to show Google+ posts in SERPS!