In my opinion Google have failed badly already in this area. In the early days their products required different logins. The first being adwords then Adsense. Why someone didn't think.."lets plan for growth" and require one login is simply beyond me.
Now when I access my Google account I can use certain products, but there are still some offerings were I need to login separately. I have attempted to merge accounts and this has caused nothing but headaches. I was told by Google support that there where some products that would not be merged within my Google account.
I think there is only really one net company that got this right and that was Yahoo!