It's getting better, but StackOverflow is still pretty dominated by C# and .Net questions. If you're using something else there is a significantly smaller chance that they'll turn up in your search results.
Check out the "Tags" page to see the popularity of various technologies on StackOverflow. Although C# and .NET are pretty popular on StackOverflow, I don't think they are disproportionate to their overall popularity in the developer community.
Look at how StackOverflow has displaced Experts Exchange, though, and it tells a clearer story:
I've been watching that over time, as a potential data source for http://LangPop.com , and StackOverflow has definitely "improved", but it has historically had a .net/c# bias compared to what turns up elsewhere, just like github has had a Ruby bias, which is slowly fading as github gains in popularity with the developer population at large.
Joel and Jeff don't create the content for the site, the communities do. The fact that other communities haven't moved into their sections en masse is not their fault. It's YOUR (ie. everyone else) FAULT.
For example, I tried to get the Grails community to use StackOverFlow when the site first started and their attitude was that they would rather just use the mailing list and sift through Nabble.
The problem isn't with StackOverFlow, it's with the other communities refusing to adopt something new. "After all, IRC is where all the best people hang out...who needs this .Net thing..."
I'm currently learning Lisp. You wouldn't be able to get this kind of an answer on a mailing list or on IRC.
"The fact that other communities haven't moved into their sections en masse is not their fault. It's YOUR (ie. everyone else) FAULT."
The first sentence is fine. The second not so much. "Fault" assumes that moving to SO/contributing etc is unambigously a good thing. I would not be suprised if at least some developers thought their existing communication channels are just fine.
"For example, I tried to get the Grails community to use StackOverFlow when the site first started and their attitude was that they would rather just use the mailing list and sift through Nabble.
"The problem isn't with StackOverFlow, it's with the other communities refusing to adopt something new."
They may have good reasons to do so. Just because you are enthusiastic about SO doesn't mean everyone has to be.
(Due Disclosure : I don't use SO at all. I once saw an algorithm question on SO I could answer and when I tried, I found out I had to use OpenID to log in. Couldn't be bothered.)
StackOverFlow provides structure and organization to the information. I've dug through enough email threads that ended at a dead-end to be able to say that the structure is welcome.
People tag their questions, while others vote on the questions and answers. Question titles are matched against the database when people enter new questions. Admins "close" duplicates, and stop trolling. The reputation "economy" provides a way to get an answer.
StackOverflow isn't perfect but it is a big step forward in organizing the information so that that the data can be searched more effectively.
The word "fault" implies that there is a problem that needs fixing.
The Perl community has a decade of history and over 800,000 posts of history invested in http://www.perlmonks.org/. Granted the site is creaking and could use a better design, but someone with a Perl question is likely still better off going there than to StackOverFlow.
The glass is half empty? I think you're completely missing the point. It's really up to each community (Haskell, Lisp, Scala, Clojure, etc.) to develop their appropriate sections of StackOverFlow. I've been on an Lisp bent lately, mainly Emacs Lisp. Think of a good question and ask it. You'll be throwing down breadcrumbs for the next guy who wants to learn an esoteric language. I've got 86 questions, and the last dozen have been mainly about Lisp, of some flavor.
Look at how StackOverflow has displaced Experts Exchange, though, and it tells a clearer story:
http://www.alexa.com/siteinfo/stackoverflow.com+experts-exch...
I don't think there is ANY other general-audience programming site with more traffic.