Usually I have exhausted web searching before I ask a question on Stackoverflow. A web search might take a bit of hunting but if the resource is to hand it is normally quicker to find it on the web than to get an answer off SO.
Usually I have to resort to SO to ask questions along the line of 'is [obscure thing] possible, if so how'. Questions of the form 'how do I do xyz' or 'what's the meaning of such and such an error message' are often quite amenable to keyword searching on google.
However, some topics are just not well documented in general. For example, I see an awful lot of 'how would I go about doing xxx' type questions relating to WPF/WCF. This incidence of questions on these topics suggests that:
- The available documentation and web resources on these topics are somewhat lacking.
- Oblique approaches are often needed to do basic stuff with these technologies.
- There is a significant paradigm shift from earlier technologies.
In this case, SO may actually be one of the more significant help forums available for these topics.