I will have to hire someone in the next few months, and seeing that the person participates in the software community is a huge +1 on that end. Seeing that they have intelligent ways to solve problems, work with others respectfully, and have the courage to admit there's something they don't know-- but know how to ask for help... that's really attractive. Am I great in all the areas I mentioned? Not as well as I'd like to be, but it's part of growing. If you can show that you're always growing by linking to SO, go for it.

Don't put "I have over 9000 rep on SO." but explain what you have. I'm not a fan of paper resumes, I'd like to see a web presence with online portfolio (which isn't always easy to do, I understand), but if you have to stick it on paper, put it under "Professional Communities," where you have a table of communities you are inolved with, for example,

 Community | description | involvement Stack Exchange | A community of software professionals | I have participated in over 400 discussions on highly-technical issues, ranging from <your best two options here>. EFF | Down with the man | I'm stalking politicians against NN in my blog FSF | Free as in beer | I edit the man pages for YetAnotherY. The Y stands for YetAnotherY.