I totally agree on an "additional info" - I usually treat it as a published paper or journal article that way - since I'm not an academic, it's not a major part of the "what I've done" section, it's more of a minor highlight.
I've also put in a little blurb, as often my reviewer is not likely to be a Stack Exchange user - I generally hover in the space between geek and management, so I have to assume my hiring manager may be quite far away from current sites with day to day answers. So I often put a blurb that explains why one should click the link:
Ranked within the top 20% of contributors in the IT Security Stack Exchange, a Q&A site for IT Security professionals. Profile found here:
Because I always update my resume to send to a specific opportunity, I generally trim and tweak. For example, my personal contributions to Programmers are quite managerial, as are my contributions here... so I only put them on for management jobs, I may strip it for high level independant contributor IT Security work. And I keep an eye on my ratings to find a good way to highlight my engagement with the community. Regardless of ranking, I can usually find something cool to call out.
On my most recent job change, after talking with the hiring manager for a phone screen, I got the sense that he was particularly interested in my management style and my take on how teams should be run and what the manager/team member relationship should be. (It turns out the team had experienced quite a bit of heartache the previous year and it was a major priority to get a solid collaborative manager on the team) Having gotten the sense of that, I sent a followup thank you email with a link to my profile that highlights my major answers. I voiced it as:
It was great speaking with you yesterday, I liked
your organization. As we were talking, I got the sense that having
strong managerial skills is a priority for this role. If you are
interested, here is a link to my writing on topics of team and
<insert link to my profile>.
I have no idea if my future boss clicked on it (I'll have to ask him) but it did the trick. I was the only candidate who got a callback and I got the job. It's been great! :)