If you google "Social Media Legalities and Workplace Policies" you'll find a virtual mishmash of conflicting advice and opinions. My opinion: keep your professional and personal affairs seperate. Your employer doesn't want you on social media but you want to have your say on a blog or twitter? Establish an alternate identity. Think Batman, Superman: "secret identity." As long as you don't link it to anything that leads back to you and your employer, you'll be fine.
Personally, I've mellowed out in my approach to social media. And I've been blogging less, enjoying it more since I stopped fretting over all things Google. As for facebook, you either need to uber-privatize it and make it difficult to access or simply stay off it. So the best advice is AVOID being seen and found by anyone save for a special trusted few.
Back to blogging for a second: despite my enormous body of work, more than 6-thousand posts here on my blogspot blog, the very best has sunk to the level of "digital waste." Posts I now consider "throwaways" are attracting search engine traffic, while the quality stuff I write that supposedly corresponds to the new parameters google reportedly considers when indexing blog posts doesn't even get a nod from the mighty search giant.