deadsea - 1:56 pm on Jun 1, 2012 (gmt 0)
We did not consider a user a bounce if the user added to the shopping cart, clicked on an ad, clicked to read a full review (as opposed to the first couple paragraphs that are featured on the product page), moved the map, or otherwise interacted with the site. It is easy to imagine why user reviews would make users more comfortable doing these things as opposed to hitting th back button and returning to the SERPs.
I'm not a big fan of hiding content with CSS at all. I rarely find that it is good for users compared to putting extra content below the fold and letting users scroll to it. For very long reviews (500+ words), you probably need to have a "click here to read the full review" so that your product page isn't dominated by a single review. Either CSS, or another page is fine at that point. I would certainly put a summary of the reviews above the fold. Something like "10 users reviewed this product and gave it 4 out of 5 stars on average, click here to read reviews". Also consider summaries of the most helpful reviews above the fold. When in doubt, copy Amazon, they do it 85% right, IMO.