Q (as in "qemu for running OpenBSD on Mac OS X")
For those too lazy to dual boot OpenBSD on their Intel Mac hardware, I found another solution to run OpenBSD in emulation: Q (as in "qemu on Mac OS X") will boot OpenBSD just fine. Previously I had tried VirtualBox, which shows problems in disk access from OpenBSD as guest OS. Since Q is another open source alternative, there's no need to spend large amounts of playmoney for this software, and you can still go and test your favorite ports to make wiwi happy!
Speed seemed reasonable. I didn't do anything heavy yet - actually I didn't do much at all - but there did not seem to be any of the slight lag you sometimes get with emulation / virtual machines.
I didn't have to do anything special to get Q to run OpenBSD. Booted from the 4.2 installer CD disk image (leeched off wiwi's mirror, ofcoz). After playing around a bit with xorgconfig I got X to work almost reasonably. I say "almost", because it does not want to give me the macbook's native resolution of 1280x800, so fullscreen mode looks warped. I haven't completely figured out what I can and can't do with networking either. We'll see.
Oh, yeah, here is a dmesg too, scp'ed directly from the virtual machine.