To a degree, the MORE info is out there, the safer you (or your privacy) is. Because eventually it becomes overwhelming, and you just get "lost in the noise". Unless of course, someone KNOWS what they're looking for on or about you.
And in that case, if they know what they want, and they were sufficiently motivated to begin with, there's plenty of ways to get all that scary and private information the "old fashioned" way. (public tax records, going through your garbage... whatever...)
IMO, the danger will come in when computer expert systems can start
sussing out the things about people that you didn't even know to ask in the first place. Then it'll truly be time for tinfoil..
I fail to see what can be done with a MAC address, and I know a bit about networking.
A lot of ISP's run multiple layers of LAT/NAT, and don't give out a "public" address for a user's connection or session until several steps away from their home, business, or the coffee shop etc. Depending on what you're trying to do, it becomes hard to identify someone if they're running through LAT/NAT and a bunch of 192.168.xxx.xxx, or 10.1.xxx.xxx internal private subnets.
If you know the MAC, you can still identify computer hardware by activity or by location in some circumstances.
http://en.wikipedia.org/wiki/Address_Resolution_ProtocolAnd it also makes all sorts of other stuff possible. Especially when you consider that 90% of the worlds "computers" are, or soon will be things like netbooks, iPads, phones/PDA's etc. that move about
constantly. And not all of them may have OS's that allow for cookies etc. for Google to figure out who you are.
Ostensibly this is to be
helpful. Say you have a iPhone or similar that was using WiFi part of the time, and the 3G network at others, and you have cookies disabled in your Safari mobile browser etc.
Google wants to get around that. They want to be able to say "
Hey! You're the same MAC address! You wanna see a listing of all the sex-toy shops and massage parlors within a five mile radius of your CURRENT location again?" etc. etc. etc...
Of course the darker side of such "help" is not difficult to imagine.