Recently, I managed to get an invitation from Stackoverflow Careers. In this post, I'll try to compare it with LinkedIn from my own perspective, a software engineer's perspective, and eventually you'll see why SO Careers is better.
SO Careers is actually a hiring/job ad platform for real developers and companies that willing to hire real developers. To get an invitation, one must prove to be a developer. It can be done in several ways. One of them, the one I used, is providing your Stackoverflow account and the system decides that whether you are a developer or not by judging from your reputation. Another one is providing a GitHub account, which I assume controls commit and contribution amount to decide. There are other options, but I think these two are relatively important and worth to mention.
Creating profile in SO Careers is similar to LinkedIn at first. Providing job experience, education background, etc. are all similar to creating a CV, like Career101. Then you feel the difference. For each experience item, besides the item description, you can specify tags, just like you do while asking questions. By that way, the item is well described and easy to judge. One can say there are skills in LinkedIn, which can be endorsed, then the one is wrong. While I'm looking at a profile, I don't care about the skill that's added for a two month job five years ago, endorsed by plenty of people I don't even know and care. I would want to see if there are common parts in various jobs, which is the longest used skill, which would be the owner has experience.
You can add your open source projects to your profile easily, easier than LinkedIn. You can link to your GitHub, Bitbucket, and other accounts. There is a part where you can specify your top answers in Stackoverflow. You can add the books you have read, the articles or books you have published. A lot of cool stuff that is not anywhere in LinkedIn.
Job openings are a lot better. if you look at one of them, you'll see there are plenty of information without any cluttering, and more information at a first glance, like health insurance, relocation, remote working, stock options, etc.
LinkedIn tries to be a social platform and fails miserably. While trying to be one, they ignore other improvable parts. SO Careers fills this gap, leaves social communication to real social platforms, and just meets employers and employees. Of course, SO Careers is for developers and LinkedIn has a wider audience. Although that's a fact, with the vision they have I believe SO Careers can go beyond LinkedIn's user base.
That's all from me, thanks for reading. Finally, here is the profile I created :)