The apps/API team here at Shopify recently started providing API support through our tag on Stack Overflow. This replaced our previous setup, which was a Google Group. I'd like to explain a little bit about the descision to go this route as well as the aftermath.
The big reason for moving to SO was to get questions in front of a much larger technical audience. We've never had trouble answering Shopify-specific queries ourselves, but a lot of the time questions boil down to something that's actually outside our scope as API maintainers to answer. Here's an example:
I'm trying to write a Rails app using the Shopify API. How should I store the OAuth access token once it's been granted?
Whilst the issue touches on the Shopify API the meat of the problem is about Rails and OAuth conventions in general. It could be answered by anyone with Rails and/or OAuth experience. Because Stack Overflow has orders of magnitude more users than we have subscribers to our mailing list, someone with the relevant knowledge to answer is likely to do so much sooner and with better clarity. This allows us to focus our time and effort on throughly answering questions specific to our core competancy. In addition, anyone writing apps in their favourite niche language (Scala, Haskell, .NET, whatever) is infinitely more likely to get an answer as our range of programming knowlege only goes so far.
The second thing is that it's much easier for the best answer to bubble up and be placed prominently for future reference. If you've ever read a troubleshooting thread on a forum or mailing list you'll know that you often have to read the whole thing from top to bottom before the solution becomes clear. SO is built around the idea that there is one 'correct' answer and that this should be shown first and foremost. It's also possible to edit SO answers so that solutions are concise, error-free, and not presented as back-and-forth conversations.
Downsides and Solutions
Naturally there are downsides with the move. The most obvious one is that we lose the direct public communication channel between develoeprs and Shopify. Because of that we're not abandoning the mailing list entirely but rather repurposing it. We've renamed the list from shopify-api to shopify-app-discuss and relaunched it as a place for developers to discuss the business-oriented aspects of app design. How much should I charge for my app? What's the best way to publicize my new release to customers? How to I get feedback? All these topics still have a home in the new list. Take a look at it here.
We also want to make sure that developers are kept abreast of news and updates regarding the API and the app eco-system. To do this we're writing periodic newsletters with info on the goings-on here in the API space.
Since we've officially started supporting Stack Overflow as our support channel (12 days ago at the time of writing) we've had 26 questions and all but 2 of those have answers. There's definitely been a wider range of people answering questions too.
Overall, we're really pleased with how the first couple of weeks have gone. It remains to be seen whether we will lose some of the community elements that we had but with the extra measures we're putting in place to keep people informed I hope that it's not going to be an issue.
If you're providing developer-to-developer support for anything, I'd definitely recommend setting up a Stack Overflow tag and encouraging people to use it. You'll end up with a curated, well-answered repository of questions that are highly visible and available in a familiar environment for developers to access.