Since upgrading a few systems from 1.5 to 1.6, we're seeing something really 
weird - gigantic runs of 0xFF in /var/log/messages.  As best we can figure 
out, attempts to read the kernel's message log (via /dev/klog (i.e. syslogd) 
and sysctl(KERN_MSGBUF) (i.e. dmesg)) are actually returning these bytes, 
about 1.5MB of them in one big chunk.  We run with options 
MSGBUFSIZE=2097152, so that leaves 512KB of readable data in the log buffer.

Have we hit some undocumented limit?  "man 4 options" doesn't mention one, and 
a day or so of reading things like kern/subr_log.c, arch/i386/i386/machdep.c 
and arch/i386/i386/pmap.c haven't done anything except convinced us we don't 
know what's going on with the kernel log.  :-)
-- 
Ross A. Patterson
Chief Technology Officer
CatchFIRE Systems, Inc.
5885 Trinity Parkway, Suite 220
Centreville, VA  20120
(703) 563-4164