Briefly, you should not take them seriously at all. Except perhaps as a market of suckers to whom you can sell junky products of your own ("Advanced Twitter Strategy Course, open only to people who are already High Klout Social Media Gurus!!").

You should mercilessly make fun of them until they get mad, post an ill-judged blog rant, and self-destruct right in front of what they think is an admiring tribe, but is really an audience of gawkers viciously waiting for a train wreck. SMGs are only good as entertaining victims of self-destruction train-wrecks.

Contrast this term with a more credible kind of guru, Unix Guru.

Why does Social Media Guru suggest douchebag but Unix Guru an actual expert? The latter:

1. Is testable. You can ask someone to do something that you can scope and define and understand, but not do yourself. Like write a shell script plus cron job that downloads, appropriately greps using a complex regex pattern, and emails you relevant headlines from 10 newspapers every day. I can define this, but I don't know how to do this. By contrast, an SMG cannot promise anything that is meaningfully useful, testable AND clearly out of the range of expertise of whoever is asking. If it is testable (I'll get you 100 retweets) it generally isn't meaningfully useful, and if it is useful (I'll increase the visibility of your product and strengthen the brand) it isn't testable. If it is both testable and useful, it is unlikely that you cannot do it yourself.
2. Is based on an actual hard-to-acquire skill. There are just too many ways to create an appearance of "social media guru" that have nothing to do with practice, knowledge and skill. You can follow-and-dump by brute force to create a good-looking Twitter profile for example. Social media is FULL of such game-able substitutes for skill. The only thing that even comes close to an actual skill is SEO, and it is revealing that it is the only subset of SMG-dom that is credible (SEO guru). Everything else is either bs or a skill from another domain (like writing, programming, video-making, photography, artwork or A/B testing...).
3. Does not need selling. Marketing is when they call you, sales is when you call them. SMG's need to call others and persuade them of their value. And once they acquire customers, they have to work hard to retain them because they are constantly combating the (correct) suspicion that the person is doing nothing useful. True guru types are generally marketing types. They attract people rather than having to cold-call or prospect for them. They have to fire customers instead of having to work hard to retain them. You go to the Unix Guru, sitting bearded in his dark cave, when you want certain dark magic things done. He doesn't have to cold call hundreds of people to stay busy. If you bug him too much, he'll start ignoring you. All gurus (including the prototypical forest-dwelling spiritual guide type), if credible, are of this sort. So ask yourself, when was the last time you actually felt the need to approach one of these SMG's for something? Chances are, they called you. You didn't call them. Most social media stuff, frankly, is not hard. You can figure it all out with some trial and error and reading up on a few helpful tutorials here and there. If you are having trouble figuring out how to sign up for Twitter, you need basic computer literacy training from a kindergarten teacher type. Not advice from a guru (the term usually denotes people who offer advanced levels of education and help, not babysitting).

So the term is vacuous. Any substance generally belongs in the much more "business guru" camp (and there are real business gurus in my sense of the term, people who are massively oversubscribed and forced to turn away people eager to give them money).