Social networking sites like MySpace and LinkedIn have consistently grown in popularity (measured of course, in the amount of users that they have).

But are they about to hit an adoption plateau?

Some people think so — and they’re concluding that the next logical step for social networking is opening up their data so that other sites can use it (the original BusinessWeek article is here).

Certainly, a critical element of YouTube’s success in building its user base has been the fact that you can post a YouTube video anywhere — it’s hard to imagine YouTube without that feature.

Yet YouTube has a very appealing and specific type of content (video) that people are willing and interested in reproducing on their own sites — but who’s going to want to post someone else’s LinkedIn information?

And more importantly — YouTube is not a social networking site. While there is a social component to YouTube, being social and connecting with others is not its primary purpose.

For the record, I’m definitely for opening up the data (in a secure way, obviously) that’s on social networking sites, which would be a mutually beneficial proposition both for users and for the sites themselves.

Yet in the BusinessWeek article, they cite eBay as an example of open social networking’s potential:

“Social-networking sites are realizing that if they want to grow their user base—and build a sustainable business model—they need to attract third-party developers. “Social networks have reached a point of maturity, and opening APIs will help them grow,” explains Adam Trachtenberg, a senior manager for eBay (EBAY). The auction powerhouse made its software available so others could easily link to its site. Today, some 40% of its listings are actually posted on other Web sites, providing eBay with billions in revenue from fees.”

Like YouTube however, eBay is not a social networking site either — eBay’s primary purpose is to connect people to purchases, not people to people (yes, they usually connect to people through purchasing, but that’s like saying going to the mall is social networking too).

BusinessWeek’s point about open standards and reusable data makes sense — but let’s not start calling everything that involves two or more people interacting ’social networking’.

Social networking has a specific meaning, and the dilution of social networking’s cache is much more of a danger to social networking sites than closing themselves off from data reuse.

Predictions about what’s going to happen on the web always seem to include a social media or social networking component, but let’s just remember what social networking is (and what it’s not).