Personally, I don't think it belongs on a business site. I actually just had a meeting with a client the other day for SEO work and they had Google Adwords on their site. They were pretty much posting links directly to their competition and getting $0.10 a click or something minimal. They sold software that retails at $5k per seat and many companies need 5-50 seats.
While I can understand the desire to make extra money, I don't believe it has a place on their site. On a blog? Not a problem. On a brochure type site? Not really professional. They may as well have had 4 flashing 468x60 banners and blink text on their site.
Some online stores can get away with it, but for the majority of sites, especially hosting companies, I think it would be a very bad idea. Think of it this way - have you ever walked into a store, ad within the first 5 feet you're given a flyer and told to leave the store that another place has the same item for cheaper? It's just like that - it's simply not, and shouldn't be done.
Amazon is a different beast, but for the most part their links all point to other parts of their site. I was just on the site right now looking for where they post Adsense information, but I couldn't find it. Anyone want to post a clue to where it's located, or have they integrated it that well that you can't tell it's an advertisement?