It's rather obnoxious. I suppose some people are really, really, into pets. (Or more cynically, guys have a better pickup rate if they have a dog in public?) But it seems like a popular option these days to show how cool a work environment is.

At one SF shared workspace area, this guy always brought his dog in. Damn thing would go sniffing around and most people thought it was cute. I found it very annoying, especially when I had food. While I could tell him to piss off and keep his dog away, then I'd come off as the dick.