Spolsky and Atwood had a podcast when they were putting Stackoverflow together and they talk at length about what they wanted to achieve. Its amazing actually to see they had a very precise idea of what they wanted to do and they absolutely hit their own objective.
Podcast 1, April 2008
https://stackoverflow.fogbugz.com/default.asp?W6
One thing we are noticing is that the book market, the programming book market has just completely vanished. It is falling apart, catastrophically. The programmers I know don't really learn new technologies from a book any more. What they do is they find a tutorial on the web -- maybe -- and they try to do something and then they page fault in knowledge. Basically, they get stuck on something and they either post to a discussion group, or they type their question into Google.
And those are the two things we want to serve basically is the posting to the discussion group and typing things into Google. Our longer term goal, if we’re successful, is that you're trying to figure out how to do something in Python like how to merge two arrays in Python and you go to Google and you type "merge two arrays python" and submit that, and our goal is to be the number one hit that comes up with a really good edited answer to that question that some individual has contributed and maybe other individuals have edited.
-----
So then you go search on the Internet for "Mac remote desktop connection beta expired" and you get all kinds of discussions; people discussing what to do and how to work around this problem, and "how stupid is Microsoft that they can't solve this problem." What's interesting is that within five days Microsoft had indeed released a new version of it with the expiration removed. So, it is still the beta because they’re still late but it’s not actually telling you that it’s expired anymore.
So that's fine, but here's the point: in the mean time, all those previous blog articles about this thing being removed are still the results you're getting from Google. And so the number one result from Google doesn’t know about the new thing – the fix. In other words, there is something that happens when something is broken and then gets fixed. The brokenness gets into Google and gets page ranked and that tends to sort of dominate the results for a long time because it’s got the earliest dates on it and a lot of the times you're trying to solve something and you find a discussion on the Internet that says "the solution to this problem is there is no solution and you are borked" and you can't do anything about it. And that's wrong, that's no longer correct, you're not looking at the correct information anymore.
One of our goals is to have a place where if somebody posts a wrong answer or they post an answer that used to be right but it becomes wrong that there is a way to remove that and to get that out of the site and to get the new right answer at the top of the page.
--------------------
Podcast 4, May 2008
https://stackoverflow.fogbugz.com/default.asp?W781
So what are we actually going to bring to the table that actually makes us better, or at least different, than these other programming communities? And I think one of the things we have going for us - and it sounds kinda obvious - is when we have pretty large audiences that we're gonna say, "Hey take a look at this thing we're doing." Right, so... you know, it's kind of like when Nine Inch Nails did digital music distribution, and when Radiohead did digital music distribution, all the commentators, when they talked about that, said, "Yeah, that's no problem, you can do exactly what they did if you have a band. Just one: be Radiohead, right, two: put digital music online." So, we've built up...
... Yes, yes, so we're hoping that having large audiences that we're involving in this process, through this podcast and through the blog and so forth, is one of the reasons that it's going to be different...
------
Spolsky: So that was the question, I guess, that everybody keeps asking, "why another one, and how are you going to hit that so called critical mass?"
Atwood: Right, well, first a bit of terminology. So, it's not exactly a forum. I mean, when I thought about this and Joel and I were initially talking about this, I framed my mind in a way that said, "OK, this is a forum that we're building." But the more we looked at it, it's not really a forum. It's more focused than that. Cause forums have a problem, and I've discussed this on previous podcasts, where you can talk about anything, right? And that ends up sort of, you end up chasing your tail in some way. When you can discuss anything, you end up discussing nothing. So, there's a very laser-tight focus on question/answer that I think sets us apart from forums right out of the gate. And then also, and I don't think we've actually discussed this publicly, but there's going to be a Wiki-like aspect to the pages as well. So the questions won't, hopefully won't go totally stale over time. Because once you get enough trust in the system, you'll actually be able to update the questions, point people to different areas as questions get old, and so on. So those are my first two observations out of the gate. What would you say, Joel?
----
See also this "Google Tech Talk" by Joel Spolsky in April 2009 when he talks in detail about the design decisions they made with StackOverflow - https://www.youtube.com/watch?v=NWHfY_lvKIQ - again they knew exactly what they were trying to do