I spend a lot of time at it, though hopefully not too much. Maybe 5-10% of my working day.

You absolutely must start with a blog or a website for your home base. Then you go to YComb, LinkedIn, Stackoverflow, and ask and answer questions. Be sure to use the same user name for as many sites as you can so you become recognizable. First initial, last name is actually preferable - when dealing with your field you don't want to hide behind an anonymous user name (like AnM8tR - groan....). You can use fancy user name for movie sites.

I use http://clubajax.org to write my blogs, and while they are informative blogs, I learn an incredible amount; because I do research before hand to ensure that I'm giving correct advice.