Is it a catastrophic problem? It is probably not, but it will become a headache in some instances. Eventually, employers will use the rep as a way of validating people's abilities. Now will the good companies do so, like Google, MS, Apple? They will not, but only the top .01 percent of developers work at those places. It doesn't matter whether or not an employer has heard of SO, because when the candidate brings it up, most will use it as a way to validate they are making the right hiring decision. They will because there is a fundamental problem with hiring people: You can only tell if someone is as smart/knowledgeable as you.
Once someone passes your abilities, you have to take it on faith what they are saying is correct. (I remember one story where a consultant mentioned some absurd comment about the stack and the heap to a tech manager about Java to show is technical prowess. Sounding good, the manager bought it, and he became the architect, of the C# applications.) I guarantee that most hiring people aren't going to take the time to look through posts and determine if the person is really as smart as they appear (they might not even be able to).
(Here's my disclaimer, I work in this industry. I work for a company who's sole job is to provide tests to determine people's profiles and competency in areas). 90% of the time, hiring people want a score so they can look at other people's scores and rate them. Now I know what you are thinking, "I wouldn't do that." I wouldn't either, but I'm not the person who makes hiring decisions. Most places don't function like MS where you are interviewed by 6 people and all have to say yes to get hired. It's a look at the resume, an interview and maybe a second interview and the decision is made. You can always not work at places that act that way, and maybe you can steer clear of them, but every time I've gone to work somewhere, there have always been skeletons in the closet, I didn't catch during the interview.
Truthfully, there is no way to stop companies from using rep as a way of showing ability. The only way is to not have it. Maybe that's O.K. that employers will use it. Someone who has a rep at least is looking at a tech site and reading it which is more than I can say for people I've work with in the past. Does that mean they are any good, nope, but if it is all they have to go on, it's better than nothing.