Date doesn't seem to be able to handle its own output. To wit:

	anthony@bohr:anthony$ date -d `date -Is`
	date: invalid date `2002-09-30T19:31:06-0400'

- -- System Information
Debian Release: testing/unstable
Architecture: i386
Kernel: Linux bohr 2.4.16 #2 SMP Wed Nov 28 05:25:00 EST 2001 i686
Locale: LANG=en_US, LC_CTYPE=en_US

Versions of packages shellutils depends on:
hi  libc6                        2.2.5-14.3  GNU C Library: Shared libraries an
ii  login                        20000902-12 System login tools
iD8DBQE9mN7o+z+IwlXqWf4RAo1rAJ4+P3ZBKaUR1HroyEK+q86Yt56RhwCgghix
ZmHiCPBVzTKyuoRcJWMu0cc=
=/gnk
-----END PGP SIGNATURE-----