There seems to be a case of split personality going on in a lot of companies. On the one hand, the blocking of social media sites continues apace. On the other hand, the adoption of social media in the enterprise is also on a growth spurt.

McAfee, the security company, is out with a study that concludes that one-third of bosses block employee access to music downloading sites like iTunes to dating sites. A quarter block access to sites like YouTube. More than half wish they could block access to social networking sites like MySpace and Facebook, but only 20% have taken the step. McAfee suggests the rest have resisted because the sites are actually used for work-related communication. Kudos to McAfee Avert Labs Security Strategist Toralv Dirro, who tossed off this wonderful quote:

The lines between work and play are blurring… but putting fair-usage policies in place and educating people on how to be safe on these sites is the most realistic option.

That’s pretty enlightened for a security software company. It’ll be a cold day in hell before we hear similar quotes from the fearmongers at Websense.

According to surveys from Barracuda Networks, two-thirds of companies plan to restrict access to the Net over the next year, an increase of nearly 23% over this year. About half of the company’s customers already block access to social networking sites (25% block just MySpace, 6.3% block just Facebook, and 19.3% block both).

Meanwhile, the prospects for adoption of social media behind the firewall as part of a company’s intranet seem to be gaining momentum. SocialText secured $9.5 million in venture capital from its existing investors concurrent with the arrival of former Adobe and Cisco exec Eugene Lee as the company’s new CEO. (Founder Ross Mayfield is sticking around as president and chairman.) Ferris Research analyst David Ferris told InternetNews.com, “There is a strong interest in wikis in corporate environments, and most tools don’t give you the features Socialtext offers, like access controls, which are really important in the corporate space.”

There’s more: The Radicati Group has projected the market for “business social software” at $920 million this year, growing to $3 billion in four short years.

At some point, companies are going to have to come to terms with the fact that networks cross organizational boundaries and that open access—governed by clearly-communicated policies—will produce benefits that far outweigh the costs and risks. Companies that understand this sooner—like Serena Software, which has embraced Facebook as a resource for employees—are likely to gain a competitive edge over those businesses too busy quaking in their boots over the bogus issue of lost productivity.