The incentive to join google would have to be the ease of use factor.

I use google as my home page (as do many people), I also use gmail, and I would probably use Gbuy as well.

Now if I could open up my browser and auto log in to my google home page and see my email, Gbuy and the web, how much easier would that be? To keep everything in one place?

Kinda like MSN home but without the added pain of it having any thing to do with Microsoft.

If Google market ANY product well enough and give people wheat they want Then I think Google could be a very major force in the internet market place.