I do not own many of them, but I do own some! The things that I love about them most are they give you the chance to "Own The Market" for the specific product. Secondly, adding the .com with the product name can create an instant Brand! You can read more about what I mean from the Q&A on Elloit Silver’s blog with Jeff Reynolds, the owner of AmericanFlags.com .
Each product domain name is different though. Many have a plural version as well. With AmericanFlags.com you also have AmericanFlag.com . In that case, one is more likely a better "search term" (non plural), but for an online store that is going to be selling more then one flag, the plural is better. In a perfect world, it’s best to own the plural and nonplural.
The down side, many products have many names. Let’s use a domain that I am currently tossing around idea’s of building a brand out of.
RecycleBox.com . Some call it a Recycle Box, some call it a Recycle Bin. Recycle container, Recycle Bins, Recycle Can etc. The most common term according to wordtracker is Recycle Bins with 193 daily searches. That is followed by the nonplural term Recycle Bin with 131 daily searches.
Now if I hear the term Recycle Bin, I think of the "blue box" ones you may have in your garage. Did I say blue box? I’m not sure why I said box, when I had just said bin. Anyway, if you are in an office setting and you hear Recycle Bin, you also may think of the Big Ass One that is outside!
Box to me sounds more personal. Like the little ones in your garage, home office or kitchen.
I think in this case, if you hear Recycle Box, the general idea is going to be about the same. It’s something that "holds recycleables".
So being the owner of the domain, I am tossing around idea’s, mainly to myself 
but by simply owning the domain name can help you create a brand, product and business!
I ask myself, should I invent (yes, I like doing that as well) a really cool Recycle Box? Should it be cardboard or plastic? Do I want to focus on a home related product or a business related product?
I could also take the invent part out and just create my own "blue box" and give it my name… RecycleBox.com ? Then people would at least know where to get one!
Troy
Speaking of generic product names.
I picked up SlimmingGels.com a couple of months ago. Good domain for the diet industry as slimming gels are a valuable product. Still haven’t done anything with it but put up a 1 page placeholder site. Even with that it ranks in the top four spots on google for the search terms “slimming gels”. I might sell it.
Troy