[timr]

Yes, that's exactly right. This kind of bundling isn't illegal until you're using a monopoly in one market to crush competitors in another market.

Microsoft used its desktop OS monopoly to ensure that IE was far and away the most dominant browser on the internet. It's a great example of how these sorts of otherwise-legal tactics, when taken to the extreme, can lead to situations that are bad for consumers -- which is why the anti-trust laws exist.

[Daniel14]

Sorry for not specifying that, thanks for the correction. The exception to promoting being legal of course is, when the product in question has a monopoly on the market. However, I doubt that's the case with Google Search. Again, IANAL, but a) the barriers to enter the industry are pretty small, b) there are plenty of alternatives, c) you can switch to them extremely easy, and d) Google would go out of business if they tried raising prices (i.e., they don't control the market).

Also, my point still stands - Google has been promoting other products on their homepage for a long time without getting sued. I don't understand how Plus would be different from, say, Reader.