Let's take a simple site,
MySpace ... Whenever you go there it will display banner ads at the top. Now those sites where banner ads come from are not related to myspace what so ever!!!
Thus, for each visit to myspace your browser has to go to one of those banner ad sites, execute a script on your computer, and download a banner ad. Thus, you are wasting time on banner ads, on some sites it could be as much as 10 additional seconds to display a page.
But it's not all about page load times, those 3rd party spamming ad companies don't care much about content. Some banner ads come with scripts that infect your computer with viruses. One name of such a virus is Voondoo, no anti Virus software will ever detected, it's very hard to clean.
Thus, because of those banner ads you don't need, you are:
a) suffering from slow browsing times
b) at risk of getting your machine infected
By the way, this is true if you are using IE, Firefox, Safari, Opera, or even Linux or Mac. There is only one way to get rid of those and keep yourself secure.
You need Firefox web browser and NOSCRIPT add-on.
NOSCRIPT add-on basically disables scripts, unless you enable them. It sounds more hassle than it really is in practice. Basically, the speed and security you get from it will outweigh all the negative things.
Firefox web browser | Faster, more secure, & customizable https://addons.mozilla.org/en-US/firefox/addon/722 
Now for the reason I'm telling you this. Answer these questions to yourself.
Why would anyone distribute a virus?
Why would anyone distribute a virus that no anti virus can detect?
Why would anti Virus companies still be unable to detect those OLD viruses two plus years after their release?
It is a money making machine scheme. They infect you, then they sell you solutions which will fix you and protect you. Above is how you break from this vicious cycle, both Firefox and noscript are free.
Believe it or not, this scheme is related to our bailouts. They are clearing the money out of us before the big boys start it with China. They want United States to loose to China during WW3. Keep in mind that we are paying 20+ mil for a single plane, while China buys a single plane from Britain for 300k. Plus there is 1+ billion of them, and only under 300 mil of us. Hope for an American revolution, or else, soon we will be at war with Pakistan and then China. I'm telling you one thing, I'm willing to spend my life fighting on the right side, but I am not fighting China or Pakistan, those wars would be wrong.
Viruses Through Banner Ads 
