I cant stress enough how EGOL has hit the nail right on the head.   You'll commonly find that most, if not about 99% of sites selling  a particular product almost always use the stock product description provided by the manufacturer.  One of the tests that I do is just take a snippet of the stock product description and paste that into Google to get a head count on just how many sites are using stock product descriptions.  This is also a good indicator on which of my competitors are paying for SEO, and if they are, what kind of in-house of firm im up against.

Creating unique product descriptions not only makes your products one of the few with a UNIQUE description, it also stands out in SE's, and almost always from what i've seen helps that particular products rankings as well, not to mention it helps increase conversions.  I know that its VERY VERY VERY time consuming, but one of the things that I like to do that i've found simplifies the process is to just record yourself describing the product, and then transcribing the recording.