We use it every time, and watch for the negatives more than the positives, since we assume the positives can easily be an employee.

Although there was a hilarious one for a B&B in Key West, where there was a bad review, and the owner did a reply that basically said, "Hey, if you don't like it, don't stay here." Needless to say, we didn't.

Also, of course, know the area: we find it funny to find reviews for hotels in the tropics where the reviewer says, "We saw 3 insects!."