goodroi - 8:40 pm on May 31, 2012 (gmt 0)
The way I see most sites using user reviews will have no significant impact on their SEO. That is because most of the sites I see have very few user reviews and the user reviews they do have are often less than 10 words long. That is just not helpful.
I like to post longer user reviews on my product pages (over 200 words). You need to get creative in how to encourage long reviews like running a contest or something else. By having longer reviews it gives good info to users so they stay longer on the page. Also I end up getting more long tail traffic since these longer user reviews will have keyword combinations that I wouldn't have thought of.