Private office for me, but not working from home. I like the social environment, but there are times when I like to close the door. This could be because I don't want to hear you, because I don't want you to hear me, or because I don't want things that I have left out getting touched/stolen.
Also, if you end up being perceived as some kind of subject matter expert, people will bug you non-stop. I like to help, but I only have so much time for that. I found that having an office raises the bar just enough that some of the more casual questions seem to go away.
Ask any experienced coder who does not have a private office if they have done the "headphones with no music on" trick.
My old manager once walked into another site's office and discovered their "open concept." He was raving about how great it was that he could ask anybody anything at any time, and everyone could have all kinds of collaboration. shudder