I would be suspicious, but then, I'm always suspicious when there's a sudden rush of reviews, especially if the burst is preceded and followed by very little activity. Look at this example:

http://tripadvisorwatch.wordpress.co...-fake-reviews/

The place in question has had a bunch of dodgy reviews removed and yet it remains top of the B&B listings in its area and it has not been penalised or red flagged:
http://www.tripadvisor.com/Tourism-g...Vacations.html

The fact that the rankings are loaded in favour of recent reviews makes it easier for dodgy owners to manipulate TripAdvisor.