I had the experience not so long ago of discovering that a senior manager not only didn't 'get' the point of a social intranet, he was positively hostile to it. He valued face to face communication very heavily and saw workplace tweeting and blogging as the pied piper that would lead people away from it. I did my best to bring him round, with arguments such as it's not a replacement, it's a supplement; that it enables people in remote offices and who work from home to feel involved, and so on. I succeeded to the point where he dropped his opposition and allowed his team to work with me to implement it.
The social intranet took off, or seemed to. But this person never contributed anything. I also noticed that nor did the majority of his colleagues on the senior team. My fear is that by working round him (and them) rather than truly getting them on board, I introduced a social intranet that will forever be stunted in its growth. It will remain OK to talk about social and/or non-controversial business topics, but serious business-related discussions - particularly where controversy is involved - won't happen.
I'm still not sure what the right course of action is when top level support isn't really there - work round, or make getting that support the first and paramount goal?