Well, at least for me (and I suspect many others).
I caught Pete Cashmore's analysis:
There are arguably better video sites than YouTube and better photo hosts than Photobucket, but network effects tend to trump technical prowess in the social networking realm.
Google Buzz certainly isn't groundbreaking, but it will achieve critical mass virtually overnight. Thanks to integration with Gmail, the new tool is in the eye-line of the millions of users who obsessively check their inboxes for new mail. ComScore pegged Gmail at 176.5 million unique visitors in December.
But I think he just narrowly missed the mark, at least for me. One critical difference is that because Buzz relies on your Gmail contacts, it creates a more focused social network; in other words, these are people that you actually communicate with already and thus content in Buzz seems to be much more relevant and interesting than Facebook.
Consider someone like my sister. She has 643 friends in Facebook. The question is what % of those people does she actually communicate with on a daily or even weekly basis? How many of those people are just incidental contacts? How many of those people are just sort of there? How many of those people does she actually care about? How many of those people would invite her to their wedding? I would guess that it's somewhere around 10-20%.
By integrating with Gmail, Google's big win is that your network is based on people that you actually communicate with. In my opinion, this makes the social network more valuable and the information much more relevant. Integration with a mail client will help the adoption rates for sure, but I think that the big win that will carry it forward as a success -- at least for users like me, who don't use Facebook as a network building or discovery tool -- is that the quality of content is much improved over Facebook.