tedster - 3:59 pm on May 17, 2013 (gmt 0)
Yes, some plug-ins have caused problems - but usually when they are in conflict with another plug-in and the combined result creates a bad situation.
Either that or the the plug-in itself has been configured poorly by the user, The answer is to be proactive about how you apply plug-ins and notice the technical changes it makes in how your website works - rather than just assume everything is going to "play well with others." There are a bajillion plug-ins available these days and assuming that all combinations are tested for any possible conflict is an "operator error" in my view.
One example, I've seen a combination of incorrectly configured plug-ins start to generate a pile of "soft 404" errors when they should not be there at all. That will gradually undermine a site over time.
You've added some common Open Graph code for social media. It doesn't look like links at all -rather it is a set of namespace declarations. That should be no problem at all, whether the code is present or not.
2 iframes in the footer
The content of an iframe lives at its own URL. So far as I know, Google has not taken iframed content into consideration for scoring the parent URL - except in the case of an iframe injection that serves malware to a hacked page.