Comment Discretion, always (Score 1) 246
Think three times before talking about, or using, anything that you learn accidentally in the course of doing your job.
You'll undoubtedly take note of office politics (although you don't necessarily talk to others about the detail, or how you came about it); office politics may well affect how you go about your job anyway, and it often helps to know where the potential traps and difficulties are, so that you can attempt to step around them.
You never, under (almost) any circumstances, discuss anything confidential that you came upon by accident and weren't entitled to know, if you do so, you are likely to find yourself looking for a new job very quickly - and quite right, too. The only exception I can think of to that would be if you were to come across something that the law or your employer would expect you to bring to an appropriate person's attention, where not doing so could land you in serious trouble if it subsequently came out that you hadn't done so. If unsure, consider covering yourself by questioning it, confidentially but in writing. Escalate, with care and tact, if not happy with the reply. And understand that, in doing so, you're not so much doing so doing so out of duty, as covering your own position.
(Putting things in writing is a good policy anyway, for almost all aspects of almost any job - NEVER assume that people will choose to remember things the way that you do, or that "nice" people won't attempt to hang you out to dry at a later date, if it serves their purpose. When you agree something verbally with someone, if it's even remotely important, drop them a note confirming YOUR understanding of what was agreed.)