I've only had a bit of time to play with my MacIvory, but already things are getting interesting.
One is getting used to the system administration style: typical UNIX system configuration resides in text files, and the boot process reads them. Genera is different. The state of the system is contained in the memory image ("world"); you change it through various operations---some interactive, some by loading Lisp files---and preserve it by saving a new world as a file, which can be defined incrementally based on an existing world. The boot process involves loading that saved file back into the living Lisp machine. I haven't yet developed the sense to complete a block of tasks before saving the world, and how much change pushes one from incremental to a complete world.
Another was getting the network to speak, and part of that is the timewarp of working in Mac OS 7, an era in which Mac networking was going through the introduction of Open Transport, and an AppleTalk era which Mac OS X refuses to acknowledge. Luckily, I've got a PowerBook G3 that runs Mac OS 9. My first ethernet card didn't work, either because I screwed up some software setting or because the hardware was bad. (More embarrassing disclosure later.) DKS sent me a replacement, which worked immediately. I've only got ChaosNet configured on the MacIvory side at this point, and my ChaosNet work isn't up-to-date on my Powerbook, so I've only seen raw ethernet packets in tcpdump, but my archaeology is already progressing---documentation to follow soon, as well as getting some Python software (with libpcap or Mac OS X kernel packet filters?) to respond to Chaos-formatted Ethernet packets.
As for the embarrasing disclosure, one of the first things I did was try to set the video card to a mode not supported by my Sony Multisync 15sf monitor. Instead of waiting for the change to timeout and revert, I hit Esc or Command-. or some other key which confirmed the change, leaving me with a blank screen. I tried various reboot, PRAM zapping, or magic key sequences to force the Radius Precision Color 24X to a good mode, but none of that worked, and at some point I screwed up the system. Once I hooked up the Dell 2007fp that understood 1152x870, I saw the floppy-with-blinking-question-mark. Recovery without a working network card involved the ancient hassles of multiple-floppy installs.
I have a Kensington ADB multi-button mouse, but all the drivers I have downloaded are either for Mac OS 8 or cause serious bugginess: system freezes or error -192 when launching the configuration application. I hope I don't have to roll my own software to get multi-button goodness to work with the Ivory. (At this date, few vendors pay much attention to 68k Macintosh support.)
UPDATE: I've captured a bit of the tcpdump results in my ChaosNET information page.