We do not advertise your ipaddress outside of your local subnet for people near me. On your local subnet your ip address is fairly well known due to various network broadcasts (ARP, DHCP, SMB,etc).
For PNRP, you register a 2^256 bit number that is only known to people who have either recieved an invite to your group or people on your local subnet.
With regard to PNM and the rest, will Microsoft be providing ways for non-Windows platforms to implement these services on things like Linux, other Unix, and OS X, the way Apple and others have with Zeroconf and Bonjour?
WS-Discovery is a WS* published protocol, PNM is implemented as any other service is using WS-Discovery.
UPnP is a Device protocol that has been supported since Windows ME, and is supported in XP and Windows Vista and is widely supported in NAT's, Printers, Media servers, and other devices. It is an open standard (http://www.upnp.org)
Zero-config is a combination of several technologies,
Auto addressing which has been supported since Windows 98,
mDNS which I believe has been superseded by LLMNR which appears to be supported in WinCe and Vista
People Near Me uses WS-Discovery over IPv6 Multicast (http://msdn.microsoft.com/library/en-us/dnglobspec/html/ws-discovery1004.pdf). Using Ipv6 allows the use of IPv6 link local addressing which avoids some of the more unplesant autoaddressing problems of Ipv4. So yes, its a published standard that also is supported by other parties.