I'm not sure whether all users happen to be as eclectic as myself and others who have meet in the other StackExchange sites but I've notice a particular awkwardness when asking questions that cross the domain of multiple StackExchange sites.
An example could be a question that is specific to English grammar and also as it applies to User Experience and as such could fit partly under english.stackexhange.com as ux.stackexchange.com but it would fit better if it could be somehow cross-listed under both.
In some cases there could be even up to three or four StackExchange sites that would make sense to collaborate with in order to properly gather the necessary folks that could best answer the question.
InterExchange Site Proposal
If I could make a proposal on a way to solve this I would suggest creating a new site called something like InterExchange.com or inter.stackexchange.com which would act as a holding area for questions that are tied to multiple stackexchange sites. The idea behind the site is that once a user is logged in they would only be able to answer questions if they belong to all of the StackExchange sites for which that question is associated with. So effectively it would allow questions to be asked in a way that require that those who answer are members in all of the necessary Q&A sites which would have a few inherent benefits which I'll try to list below.
- Answers will likely be more precise since those answering will already generally be part of the same set of StackEchange sites.
- Cases can be avoided where members of specific StackExchange sites feel like the question doesn't really fit strongly within one site or another but instead the question will instead be whether the original question belongs cross-listed and thus moved to the new inter exchange site.
To help encourage knowledgeable experts to participate in this proposed site one benefit could be that points awarded within the InterExchange site are awarded as well (perhaps partially) within the sites that a question is cross-listed under. This way questions that truely span the domain of multiple Q&A sites can be found in each cross-listed board and the users have an incentive to participate in the multiple StackExchange sites where they effectively further their reputation on multiple sites by asking and answering a single cross-listed question.
UPDATE: Perhaps instead of a new site this could just be a new function of the StackExchange.com site since it already works as a sort of gathering place for the other StackExchange related sites.