As of this week I can no longer see XKCD at my office, due to SonicWall, a content filter service my company subscribes to. It is not blocked as "Adult/Mature Content". As this is the same service some businesses that offer public wifi use (Panera Bread in particular), this may mean XKCD has been dropped from a lot of public places.SonicWall now blocks XKCD (Thanks, Nathaniel!)
I don't blame you, guy. I blame SonicWall. They're most anal about the smallest things. Only recently has my office gotten access again to MySpace, which was also listed as "Adult/Mature". principiadiscordia.com was listed as "Occult"; now it's still blocked, but listed as "Other". My best guess is that what did it for XKCD was the sexual positions strip...as far as I can tell, these people have little brain and less sense of humor.