To me it is a value proposition: what are the advantages of a service vs. disadvantages like privacy issues. I choose to use most of Google's services, occasionally use Facebook, and I am sort-of addicted to following people who I consider to be "thought leaders" on Twitter.
Also, my early take on Buzz: it is OK, but I have an attitude that I don't have to read everything that shows up on my Buzz list. Same as Twitter.
I have also started to sometimes do short tweets on Twitter, and maybe following up with something more detailed on Buzz.