GMOs, Helpful, Harmless, Harmful or Horrific?

Man has used selective breeding to get the characteristics he wants in plants and animals for hundreds of years, with some good and some harmful changes to the plant or animal in question. Some pure bred animals tend to have known issues. For example, Pomeranians were bred down from the Spitz, a Greenland/Lapland sled dog. If breeders are not careful a common malady of the Pomeranian is luxated hind patellas (dislocated back knees).

Our fruits, vegetables and grains have been selectively bred for hundreds of years to render larger yeilds, deeper, brigther or unusual colors, and probably better taste as well.

So now scientists have taken it a step further by using gene splicing methods from biotechnology to create genetically modified organisms--mostly plant foods. Is this just selective breeding taken one step further, or is this something more ominous?

I personally think there may be unintended consequences--perhaps insidious changes that add up to something...not quite right? I need to learn more about it, so I'm going to do some reading, the following books except the second (which I have already purchased for my kindle reader) are on my wish list. In the meantime, what's your take on GMOs? Helpful, Harmless, Harmful or Horrific?

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1280366/