- The file FAQ in the glibc source directory contains a section
that explains source-code incompatibilities with the old libc;
read this _first_, it will save you time.
- The /etc/utmp format of glibc is incompatible with the one of
the old libc. This is not so much a glibc feature per-se, but
H.J. wants to use this format in the future (libc-6.xx), so glibc
simply is one step ahead.
- The timezone files may have a different format, too (/etc/localtime).
Actually, I'm not sure whether they're incompatible, but you may
want to double check.
And, thanks, Mikael---excellent work!
--david