> For some reason, the presence of this 128.149.x.y entry in my /etc/ifaliases
> file causes the system to add a direct network route for all of 128.149.*.* 
> at boot time.  It never used to do this before.  So now when I reboot, I

This is because you didn't specify the netmask for the alias.

> interface 1:  fd=5,  bfd=0,  name=le0,  flags=0x1
>               sin=128.149.x.y  bcast=128.149.x.255,  mask=255.255.255.0
> interface 2:  fd=6,  bfd=0,  name=le0,  flags=0x1
>               sin=128.149.x.y+2  bcast=128.149.x.255,  mask=255.255.255.0
...
> bind() fd 9, family 2, port 123, addr 8095[x]ff, flags=0
> flags for fd 9: 0106
...
> Oct  6 03:02:42 netbsd4me xntpd[14100]: bind() fd 10, family 2, port 123, addr 8095[x]ff, in_classd=0 flags=0 fails: Address already in use

This is probably just a bug in how xntpd deals with aliases.  It
should be easy to fix.