I don't have a Facebook account, so while I think the concept of Browser Stack is awesome, I'm going to skip this entirely since setting up a Facebook account just to use it pisses me off...
No, I do not want my music taste and photographs automatically shared with a random selection of friends, strangers, and businesses. There is a slight difference between who I am and who I want other people to think I am.
Imagine my surprise at finding out that youtube was sharing my history. Along with my mostly technical interests, there was fails and a specific interest in philology!
For the moment, Facebook is rapidly cornering the market. Which is too bad, in my opinion.
[1]: Random Idea: Maybe ISPs can start issuing randomly-generated cryptographic key pairs along with an IP address. This way, a particular IP + public key would be distinguishable from the next user who gets that IP address, but would not be traceable to a particular customer (not any more so than an IP by itself), and would be used only until the customer requests a new IP.
The key would provide IP address authentication ("this IP has not been assigned to someone new since the public key is the same as before.") This would all happen transparently beneath the application layer (perhaps as an extension to TCP), so existing app-layer protocols could use it OotB. Other handy features might include detecting if a machine with a static IP has had its connection interrupted since your last visit.
Each keypair could be signed using the ISP's own private key as a protection against being spoofed. Customers would be asked to choose some sort of password/phrase/favorite number/etc. as part of their service signup, which would then be used by the ISP as part of the seed for keygen system.