Genetically modified organisms: How safe are GMO-produced goods?

Genetically modified organisms, or GMOs, are organisms that are DNA-altered and used for many consumerist reasons today. But are they safe?
GMO treatment on a corn.

Reebok Easytone Shoes | Pros and Cons

Reebok Easytone shoes, by all accounts, should work, but will they work well enough to be worth the price? Also, a pretty limiting warning comes with them...
Reebok in white text on the black sole of a shoe.