Simsi - 9:49 pm on May 31, 2012 (gmt 0)
I think if there is an impact, it will most likely be affected by the quality of the reviews. Mine (travel reviews) go into moderation and I employ a freelance editor to tidy them up grammatically prior to release. That said, in the past year I have seen no ranking impact either way that I can directly attribute to them so it's more hunch with a nod to one of the early Panda iterations that IMO seemed to impact a significant number of sites with UGC.
Oh...and we ditch the one sentence reviews incidentally unless they are very useful snippets.