One of the biggest pitfals that I see with the diversity of SO is that there is no index of sites. Sure their are the big one's at the bottom, but I had no idea that there was a site dedicated to iPhones or that we had a site for business plans. They are all hidden to everyone who doesn't constantly monitor Area 51.
What would really solve this is a list of every single big, small, private beta (just to know that they exist), and public beta site that is hosted. And if such a list already exists, the list needs to be more prominently displayed somewhere, because I have not come across such a list in months.
If we had this list and showed it off (perhaps in the FAQ, the bottom of the page, and in the Ask Question page) I think that mis-filing of questions would drop dramatically. Instead of asking a question in the wrong site not knowing that we have a dedicated site and have to face the wrath of comments and downvotes, I could simply click on this master list, see whats out there, and go to that specific community.
This list could even be expanded by listing sites in Area 51 but with a much better layout. Due to the length of such a list and the mis-conception to some users that its an actual Q&A site, it should be on a separate page.
The layout should be something like a table, with the column displaying the name/logo, and the other for listing what should be asked (taken from the FAQ). This allows for a much better finding of sites than just a list of names or the Area 51 approach of quick 5 second topics. It also needs to be on 1 page so I don't have to search through page after page of sites. Using pages would just be detrimental to the goal of limiting mis-filing, since most users don't want to search through page after page. The find feature in browsers is meant for a reason.
Sites in the list could even have dozens of tags of questions that could be asked, however it would be manually maintained due to the random tags that I sometimes see in SO. For example, if I came to the list and typed in PHP or Tomcat, I would get StackOverflow, ServerFault, and that web design site, filtering out sites like the above Business help. Quickbooks however would list the Buisness site along with StackOverflow.
What do you think?