I posted a employer ad on SO Careers, and also GitHub Jobs. The SO post resulted in a satisfyingly large set of high-quality candidates. I was satisfied with the value.
In contrast, GitHub was surprisingly disappointing. Maybe one or two worthwhile candidates, and a ton of junk. It appears that GitHub's jobs get scraped and posted elsewhere, and the bulk of responses to my ad were low-quality (and that's being generous) candidates responding to those reposted versions.
Interesting theory. What prevents other sites from scraping SO posts? If the answer is "nothing", that suggests it's just a matter of time until it's just as bad. Right?
I'm not sure, as I didn't dig too deeply. I forget the details, but I knew the post had been reposted, since many of the (poor quality) candidates said things like "I'm inquiring about the position posted at [some-place-other-than-github]"
In contrast, GitHub was surprisingly disappointing. Maybe one or two worthwhile candidates, and a ton of junk. It appears that GitHub's jobs get scraped and posted elsewhere, and the bulk of responses to my ad were low-quality (and that's being generous) candidates responding to those reposted versions.