Here's a record of my experience:

I got bit by the (now fixed) libc Makefile bug (no time functions).
Keeping backup copies of ld.so and libraries while upgrading is a Good
Idea....

mount_msdos now requires that any MSDOS partitions in the disklabel
now be labeled as such.

disklabel weirdness: Why did I get the error message "DIO????:
read-only filesystem" (can't remember the exact ioctl) when I tried to
make the change above?  The label change still stuck, so it looks like
this error is spurious.  My MS-DOS partition lives on /dev/wd0g, and I
was using "disklabel -e -r /dev/rwd0d" to alter the label.  I'll
doublecheck the ioctl name tonight if anyone's curious.
-- 
Mike Long <mike.long@analog.com>       PGP 2.6.2 public key signature:
VLSI Design Engineer                  CCBF225E7D3F7ECB2C8F7ABB15D9BE7B
Analog Devices, CPD Division
Norwood, MA 02062 USA                assert(*this!=opinionof(Analog));