The problems that the advisory is talking about refers to a bunch of very unruly young men who station themselves in the road leading up to the main gate of the Giza Plateau. They essentially assault cars, often jumping on the hoods even, trying to tell you that the plateau is closed, that you have to come with them to enter on a camel or horse and so on. I live near the area and often have to drive by. I find these men to be extremely annoying and since I drive myself and speak Arabic I just tell them to move or I will run them down, or I say nothing but drive aggressively. Theoretically, the police should be controlling these young men and there is a police station there in the area where they are making the problem, but so far no one has seen fit to tell the police to exert themselves.
Once you are inside the plateau area, the problem is not so bad at all, although all the people selling camel rides, carriage rides and silly souvenirs are a bit more pushy because the number of tourists is really low and they are having problems making money. If you are going to Giza, I'd recommend getting a good driver to take you and to help you move around the plateau as it is a huge place. Talk to your hotel and ask for a recommendation of someone.