Watching the FTC start its investigation of Google does remind me of earlier investigations of success (such as the Microsoft Explorer browser).
As I understand the law, there is nothing that prohibits a company being so successful that it has an effective monopoly and controls a significant portion of its marketplace as long as that company is doing nothing illegal in the process -- especially not preventing other companies from entering the market and customers from using competing products.
I don't think Google does either of those things except that their success feeds on itself -- the more successful they are in their search business (which is what this is all about), the harder it is for others to be successful search companies (although Microsoft's Bing is having a fair try) and the less likely users are to try a different search engine.
Note that it is not quite like the auction issue -- where the larger an on-line auction company becomes the less attractive it is to list your items on another site because fewer people will ever see it.
For niche things (fine art for auction sites), specialized topics for search engines (medical, for example), there may, in fact, be better places to go.
Google is interesting because (1) it's so big and (2) its success in search, which allows it to collect enormous revenues in ads to the searchers, funds all of the free software which attracts users to its site -- not just to search but for everyday work.
I cn't imagine an Internet without Google (although this may merely mean I'm lacking in imagination) since I have not seen a better way to find the things I seek quickly. But someone else can try and in the world of the Internet it would be possible for users to find them, in volume, quickly.
What will happen -- too soon to tell. But we will all be watching.