BumpIn.com is also doing the same. But I think that the market size is very big. Being able to comment and interact with other people on any site is the missing

BumpIn.com is also doing the same. But I think that the market size is very big. Being able to comment and interact with other people on any site is the missing feature of web 2.0. In this case that multiple players can exist together. But sooner or later something like browser wars will start.