Should I tell my postdoc advisor I'm intending to leave? I've decided to quit academia and am actively looking for other employment. Colleagues of mine have kept their postdoc advisors close as they've looked for work, but they also had close relationships with their advisors (maybe their advisors even helped out).

My advisor is only really interested in whether I'm producing a paper, so I don't see any real reason to give more than the standard 2-week/month notice once I've found a position. That is, unless there's some academic standard practice. 

What's "good practice" in terms of notification?
There's nothing standard here. Give as much notice as you can, to be nice, and as much notice as you are legally required to if that's applicable in your jurisdiction. Don't burn a bridge if you don't have to. Even though you are leaving academia, you current boss may have connections to industry that they might be willing to use to help you find a non-academic job, so it might be worth talking to them now rather than when you find something.