On 03/18/2011 08:52 AM, Somebody in the thread at some point said:

quoted

+	/* mark it as not multicast and outside official 80211 MAC namespace */
+
+	mac[0] = (mac[0]&  ~1) | 2;

so here lies the answer to my question "From where do you get the MAC" :)

Is there a guarantee that this MAC will work in all Ethernet setups?

Yeah it's in 80211 spec.  You have to buy the spec, I can't point you to 
it directly, but here is the wikipedia article showing the structure

http://en.wikipedia.org/wiki/MAC_address#Address_details

the random mac addresses generated by the kernel also use this scheme.

-Andy