I've only ever seen one drive give SMART warnings and that was a drive that was in a rather battered laptop. It did actually kind of work but had a transfer rate of about 1k/s as Windows would load but slooooowly.
All of the other dud drives I've got just died suddenly without any warning.
SMART is more for giving you a probability that the drive is going to be bad rather than actually warning you of impending failures. It basically keeps statistics e.g. power on hours, CRC errors, seek times and if the values exceed the preset thresholds then it will warn you.