An interesting thread on AirDisaster.com (including video) discusses
the false glideslope indications that nearly did in an Air New Zealand
flight some years ago. This is particularly interesting given that
the FAA no longer seems to require an outer marker or equivalent on
ILS approaches, making it much harder to check for correct glideslope
indications.

http://airdisaster.com/forums/showthread.php?t=83775

Here's an excerpt from an article linked in the 7th post in that
thread that explains why it happened:

"On the night of July 29, 2000, the glideslope sidelobe amplifier was
not operating in Apia. In addition, the ILS ground equipment had been
left in bypass mode following calibration maintenance. This prevented
system transfer to the standby transmitter. No alarm sounded in the
control tower because the cable that fed information to the tower
navigation status displays had been cut during construction. As a
result, the Air New Zealand flight received only the glideslope
carrier wave transmission, which was interpreted by the instruments as
being on glideslope, with no warning indications."