> OT reports "00:05:02:52:34:72" in the info-box and NetBSD reports upon
> boot "sn0 at nubus0 slot e address 00:a0:40:4a:2c:4e"

As Ken says, the following comment in if_sn.c explains this (as does an
Apple tech-note, indirectly):

        /*
         * For reasons known only to Apple, MAC addresses in the ethernet
         * PROM are stored in Token Ring (IEEE 802.5) format, that is
         * with all of the bits in each byte reversed (canonical bit format).
         * When the address is read out it must be reversed to ethernet format
         * before use.
         *
         * Apple has been assigned OUI's 08:00:07 and 00:a0:40. All onboard
         * ethernet addresses on 68K machines should be in one of these
         * two ranges.
         *
         * Here is where it gets complicated.
         *
         * The PMac 7200, 7500, 8500, and 9500 accidentally had the PROM
         * written in standard ethernet format. The MacOS accounted for this
         * in these systems, and did not reverse the bytes. Some other
         * networking utilities were not so forgiving, and got confused.
         * "Some" of Apple's Nubus ethernet cards also had their bits
         * burned in ethernet format.
         *
         * Apple petitioned the IEEE and was granted the 00:05:02 (bit reversal
         * of 00:a0:40) as well. As of OpenTransport 1.1.1, Apple removed
         * their workaround and now reverses the bits regardless of
         * what kind of machine it is. So PMac systems and the affected 
         * Nubus cards now use 00:05:02, instead of the 00:a0:40 for which they
         * were intended.
         * 
         * See Apple Techinfo article TECHINFO-0020552, "OpenTransport 1.1.1
         * and MacOS System 7.5.3 FAQ (10/96)" for more details.
         */

> I just came across this because my dhcp-server leased two ips to two
> different mac-addresses and I haven't much equipment lying around
> here...

I can see this being a problem at some point...

-allen