Personally, I would love it.
Most offices that allow it have policies that go with it (i.e. regarding animal behavior, accidents, etc.). I don't know how they handle the allergy issues.
Here is an interesting article on it that says 1 in 5 companies in the US allows it (done several years ago, though). I would be a little surprised if that statistic were accurate, but I suppose it's possible.
http://www.foxnews.com/story/0,2933,200460,00.html