Edit: OSX in fact doesn't do this. It appears that one of my neigbours has a large hosting company (which probably explains his $200,000 car), whoms address shows up in the https traffic I came accross... It's a bizarre coincidence though: I'm sniffing my own network traffic on a random public wifi network about 150km from home, and I notice my own address in it. The same address that I used to register my MBP. So what do I conclude from that? That my MBP must have leaked it somehow. How large is the probability that the address was in fact the address of one of my neighbours running one of the largest hosting companies of my country...?