I find that the SO-spinoffs create separate worlds that really should be united somehow, by other than just subdomain.stackexchange.com.
Both have to do with using language
These have to do with programming. I think its good they all have their separate sites, but I still get the feeling they should somehow be "bridged."
A first time user on stackoverflow.com makes his virgin post about something very web-related. That seems to belong on webmasters.stackexchange.com, but he doesn't even know about that site --
Logged in to PROGRAMMING - (super interface above stackoverflow, webdev, and all other programming related sites) [[ Ask a question ]] (text area to enter question) - Which site would you like to post it to? (radio buttons below) * stackoverflow.com (skeet skeet!) * meta.stackoverflow.com (patrolled by idiots - not recommended) * webmasters * gamedev
In general I don't think the default home page does a good job at showing sister sites (listed at the bottom). I get the feeling that there should be ONE hierarchical LEVEL above, like
-english -authors -linguists -programming -stackoverflow -programmers -web dev -gamedev
Cross posting could be allowed.