Each "port" on your desktop is a NIC. However, even then there is not a 1:1 relationship (as far as the network is concerned) between NIC / network port and MAC. I run multiple virtual machines with bridged interfaces behind a single physical NIC connected to a single switch port. Each of the bridged virtual interfaces has a randomly generated "probably unique" MAC. If you mix that with an older, hub-centric network, there is no direct association as far as the network is concerned at all. You get a series of broadcast ARPs with responses that are broadcast to every port. In this case, machine A doesn't care what network port machine B is connected to at all...just that it's in the same broadcast domain. (Reasonably modern networks are all switched)

We haven't *actually* exceeded the entire 2^48 address space. I can guarantee you that 3com has made more than 16M NICs since the beginning of time - but they have 23 OUIs to spread things around. The original *intention* was to have everything be unique...but that would require everyone playing by rules that don't actually exist. The reality is that MAC address are reused within a single mfr. I saw a handful of dupes in a shipment of 200+ 10bT NICs 15 years ago - and if I'm remembering correctly they were 3com 3c509's...not exactly some no-name brand from China.

It's still not a real problem. Your MAC address doesn't make it past the very first router it hits. It does, however, make it a poor choice for globally identifying a piece of hardware. In this case, IMEI / IMSI is the way to go.