So which one is it? Do you slack more, or less, in private space?

I personally find open space distracting. When I'm separated, I do browse a lot of HN and stuff - but at some point I eventually concentrate, gain speed, and start getting the work done. Not so in open-space; there I find it hard to do anything else than read HN or talk on IRC. Partly because I find the presence of other people unnerving and annoying when I'm working.