I am old fashioned, so I use IM to say things like "Hey, Martin, I'm thinking about ... Does it make sense?"
Not so much mailing out code reviews, but sharing design ideas, approaches, etc. Former coworkers you are still friends with, open source collaborators you have become close to, etc all work.
Basically, build and maintain relationships with people who have good judgement. Help them out, ask for help yourself.
