Are you talking about xwiki-users or xwiki-dev? I'm also curious to list the domains of discussions that you think should get separated.
Me too :> And there's the rub, of course. The variety of topics that arise is as varied as the human imagination; as such it defies categorization, especially a priori but even after long experience, because of the variety of personal perspectives and because as a community matures it changes. Any attempt to sort it all into neat categories fails for several reasons: overlap in categories; difference of perspective; ambiguity of labeling; probably many more that I can't think of. That's why, like you, I favor Google's philosophy that searching is better than filing - when the tools are available to do it effectively.
Seggregation in general is bad as it doesn't lead to cross pollination. It should be avoided at all cost unless it's no more possible to avoid it.
Here you make a very good point. I'm not certain whether this is included in what you mean by 'cross pollination' but I can certainly see a problem with a highly-segregated issue taxonomy not making the necessary connections between topic posters and monitoring listeners.
I'd rather we focus all on reducing the questions asked on the list by improving xwiki.org
A hearty Amen to that. Of course, they're not mutually exclusive, and those who find it necessary to create other mechanisms are always free to do that, and if they do, and are successful, they are very likely to contribute to the effort.