my rule is to weigh whether or not its worth making a comment very carefully. nothing without a clear justification. never say 'I would have done it this other way' - unless its a good friend who you often discuss style issues with. comment on things that you feel would make a substantial difference on schedule, maintainability, or function - and provide a clear reasoning with which to argue against.

wasting your peers time trying to enforce your style isn't just non-productive, it sours everyone on the whole exercise.