But my experience is that this sort of thing (as you observe) really rewards those who are good at writing and navigating the social waters... rather than really reflecting work. If a manager is reviewing snippets, you just need to say what he wants to hear.
Even if it should be "Was kind of blah today, didn't get any work done, talked to Y about it for a while but still didn't do much", you'd of course write "Faced several challenges with X, but made progress; had meeting with Y and got useful feedback".
It's sort of an art, especially when it comes to full performance reviews. I used to be something of a savant on the subject.
I have yet to see ANY system which comes close to measuring programmer productivity, even in a relative way, that isn't prone to huge errors or gaming.
Same problem with interviewing, really; often social adeptness is what's being measured.