Blueloo, 'threats' are supposed to be external to the crew and so from a purely academic point of view you could argue that 'being tired' is perhaps not a threat. Further, raising it as an issue to manage brings into question whether the individual is actually fit for the flight. If you put that particular point through the '60 minutes' test or the 'board of inquiry' test then it takes on a whole different life.
More often than not, on a 'normal' day my identification of threats is 'nil' and then I ask the other crew if they've got any that I've missed. This is when the trivial and pointless occasionally come to the fore.
Whilst a series of early starts, long days, etc is an issue to be managed, my major gripe is that the whole tiredness thing appears to be somewhat of a throw away line. Something to say because people are looking for something- anything- to list as a threat. I generally ask after someone brings it up exactly what strategy we're going to put in place to manage it. The answers are interesting and range from 'vigilance' to 'focus' to SOPs. I ask are when are we not vigilant and when do we not follow SOPs?
Of course my main point point is that people are jumping at shadows and going over the top to deal with a 'threat' and that whether we agree or disagree on the issue of tiredness, going looking for threats that we already have procedures in place to manage is a little pointless.