Here's the suggestion, approaching the issue of question area51 question overlap from the reader's side:
1) Create a search feature on stackexchange.com which allows searching of all the SE sites simultaneously.
2) Create a ninja search operator to pull up the same list from within an individual SE site.
Why would this be better than a Google search? Well, google searches the whole internet. This would only search the stackexchange community of sites. The advantage of that is it limits results to sites with the same trusted formats and reliable user-base. Though User IDs might not be useful, presumably, tags would be related to a limited range indicated by the question.
Last, and most relevant to the original issue, which was exploring multiple SE sites and how overlapping questions might play between them, this search would let you see where questions had already been asked. For example, a search about an online database application could explore Webapps, the SQL Q&A, and whatever other sites share an interest. Without having to visit each site separately, you could see which community has info on your query already, as well as which one might be the best place to ask it.
Background: The inspiration was this post, which raised the issue of what to do with questions which would fit on multiple SE sites. It seemed unlikely that the ability to automate cross-posting would happen any time soon, since each site has a different perspective which a questioner could individually decide was worth the extra effort to manually cross-post or not. But there's still some untapped functionality regarding harnessing questions which already exist on multiple sites.
[storage]
on Web Applications vs.[storage]
on Cooking).