On Tue, Jan 21, 2003 at 04:49:35PM -0500, Steve Bellovin wrote:
  | Given the problems sometimes reported in building -current, I prefer to 
  | do my compilation while still running the old system, so that I can do 
  | other things.
  | 
  | 	./build.sh -D /usr/netbsd
  | 
  | (Stand back, wait a while.)

This is sensible!  This is, IMNSHO, the ONLY way to update. 
You've hit the minor hitch with the scheme ...


  | Great; it built.  I reboot to single-user with the new kernel, and try 
  | to install:
  | 
  | 	./build.sh -D /usr/netbsd -i /
  | 
  | It's recompiling the world...

Yes; '-i ...' is performed after all the other operations.
The default operation is "make build", and unless you have UPDATE
set (or use build.sh -u), one of the the first things "make build"
does is "make clean".  Which removes all your hard work from the first
pass :-(

There's a couple of solutions:
	./build.sh -D /usr/netbsd -b -i /

    (`-b' only builds the "make" wrapper scripts, and doesn't do the
    "make build" step.  the documentation of this should be improved)

	./build.sh -D /usr/netbsd -u -b -i /

    (still does the "make build", but with "UPDATE" set, so the
    "make clean" doesn't run)


BTW: Where are you looking for your instructions on building? 
I would like to ensure that the various instructions on how to
build in the source and on www.netbsd.org provide useful and
consistent information, and it seems that we're probably
deficient in that at this time.