This list is probably appropriate, or current-users, and I suspect
dmesg from working systems is not really needed.  A concise
description of the hardware that it worked is useful as a continuing
sanity check, although it seems there are a lot of netbsd-4 systems
running fine these days.

Anything that doesn't work (that either used to or has been claimed to
now work) is particularly notable and relevant dmesg snippets should
be included.

  All ran fine, then when I ran the 4.0_BETA2 installer in Upgrade
  mode, some combination of me being asleep at the wheel (90-100% of
  blame) and NetBSD's residual affection for partition-type 165 as
  well as its own, native, 169 (0-10% of blame), led the 4.0_B2
  updating process to scribble most cruelly into the FreeBSD
  partition.)

Hmm, CHANGES in netbsd-4 and CHANGES.prev in current says:

	i386, amd64: remove option COMPAT_386BSD_MBRPART from default
		kernels.  NetBSD has not used partition ID 0x165 for many,
		many years, and the presence of this option in INSTALL
		kernels can cause overwriting of existing FreeBSD
		installations when sysinst writes back the disklabel.
		Those with very, very old NetBSD installations may find
		that they must update their fdisk partition tables to use
		partition ID 0x169 for their NetBSD partitions. [tls 20070124]

So perhaps the installer has a bug still.