I recently did a move to a propagate a set of reviews across the entire site (Planting the set of reviews under every product page so that people can see the reviews no matter what product they were looking at), but this had, I found, an undesirable side affect. All my pages show up as being ranked 5 stars in the google search engine results! I'm kind of afraid that I could get penalized by google, when I'm only trying to let prospective customers see all the reviews I've received. Do I have anything to worry about? Is there a way to tell Google to not look at my reviews?
Generally, you should use a separate review for every product.
In practice, this might be heavy to achieve and maintain, so that one may resort to the solution you did.
I believe this would not influence your ranking negatively or involve any penalty.
But you must understand that any negative customer feedback with a given product will influence your overall rating, as customers may expect the voting mechanism - if any - to be in relation to the product, or may even review the product on Google if you are a trusted store.
There is no need to prevent Google from indexing your reviews as Google can detect user contributed content and treats it as such. In addition you would simply need to monitor the reviews and have your own moderation toolkit in place to remove reviews that are obviously spam or appear to be affecting your Google SERP ranking.