Like many of the StackExchange sites, there is considerable overlap in the covered topics of SQA. As you mentioned, the technical side overlaps on to StackOverflow, while the procedural side overlaps onto Programmers. This is very much intentional, as it brings together the important element that the two are related, even though each site will bounce the offending questions to the other.
So to answer your question, you can post technical QA questions here or on StackOverflow. You can post procedural QA questions here or on Programmers. Just don't post technical questions on Programmers (they'll send you to SO, or maybe here) procedural questions on StackOverflow (They'll send you to P.se or here) or non-QA questions here (we'll send you to SO or P.se, or cars.SE if that's where the question belongs!)
Using SQA instead of SO/P.se
* Users are more dedicated to SQA, increasing probability of a directed answer
* Because it bridges the gap between procedural and technical topics, you're more likely to get a balanced answer here than on either of the others.
Cons to using SQA
* A smaller userbase/contentbase means longer delays in getting the answer
* Lack of community-decided standards have potential to cause some problems getting the answers you seek
The good news is that the cons are temporary and are relative to the age of the site. Indeed, each site on the StackExchange network (and every site EVER) has gone through these growing pains.
I would welcome any question you have on SQA that would have had one of the following tags on SO/P.se - that doesn't mean they aren't just as appropriate as they were before on the original site, this just means they are also welcome here.
* Selenium
* Selenium2
* QA
* testing
* test-automation
That's just off the top of my head, I'm sure there's plenty of other tags that would qualify on that list.
tl;dr - The existence of this site does not make questions any more or less appropriate on their original sites. It merely provides an alternative venue which, over time, will likely be the send-point for questions of QA nature on the original sites.