And here is the problem: Many people will admit to the behavior of just clicking on the first link that comes up (See a couple of posts above).
The worst, (and easiest to prosecute, when proven) monopoly tactic is gain a dominance over a market, and then use that dominance to gain dominance over other markets. In the US this is very illegal, because it is a inherent weakness in the basic capitalism system, that needs this kind of government protection to keep one rich King from gathering and hording all the wealth and means of production.
Google was the dominant search engine, or more realistically the Index for the Web. When they decided to make Google Maps and compete with MapQuest, they used an unfair advantage of owning the index and gaming it to their advantage.
Here's an example if you can follow: Say its 1980 (pre internet searches) and everyone is still using the Yellowpages to find all their businesses and services. What if the phone company (that owns and prints the Yellowpages) decides to buy a automotive repair shop, and starts placing its Ads as the First and biggest ad at the front of the Automotive repair listings. (See just like links, lots of people tend to just call the first person listed in the book, that's why the yellowpages charge the most for the big ads (like $10,000 back then for half page ad) and they gave seniority..whoever ran the largest ad for the longest was in the front of the listings. But the Phone company wouldn't have to pay that ad money, they could just add in their services in front for free. They could even go so far as to "loose" or make typos on their stiffest competitors. Then the phone company buys up the other failing repair shops, and expands its dominance. It would not take long before the Phone company now has a monopoly on automotive repair, if they were to repeat this tactic it would not be too long before the phone company owned every business in town, and everyone worked for them. Sure its a free country, someone could start a new phone company, or just print a new yellow pages, but the time it would take and the barrier for entry (not having everyone phone info for one) would make this unrealistic before the damage was actually done.
The fear here is that by owning the index and ad market, Google can use this dominance to keep opening up new business (cell phones, Internet Browsers, Social Media sites for example) and use their advantage of owning the index to make their business appear to be the most popular, when in fact they are not. Advertisers like this model because they only have one place to place their ads and pay money too, even if they have to pay a lot, its proven more effective that having competition, without the advertisers going to new competing search engines, those new search engines don't have an easy revenue stream to compete and actually buy thousands of servers and hosting data centers to park them in.
I think the worse tactic is Google is able to search through everyone's search results, (and the email of anyone using Gmail) and use this data to their advantage as well. They know what is popular and what people are wanting to buy and how much they will pay for it, before anyone else can. It would be like above example I gave, but pretend that the phone company could also listen in on everyone's phone calls.
Its really high time that government takes the same protection of our phone calls and letters and applies them to our searches and internet behavior... this should be private because it can be abused in a very bad way (barring a legal warrant of course to catch actual criminals)