The purpose of this page is tracking and explaining the features added in every release, just like the [http://wiki.dragonflybsd.org/index.php/DragonFly_Status Dragonfly people did].
It'd be nice if kernel hackers would spend some minutes adding their stuff here. The one place where you can find a comparable changelog are the fabulous LWN kernel articles: http://lwn.net/Kernel/, or [the http://lwn.net/Articles/driver-porting/ driver porting guide] - but there's no reason why the kernel community should embrace and extend those efforts 
TODO
Import (and extend, explain, etc) LWN's [http://lwn.net/Articles/2.6-kernel-api/ list of 2.6 API changes]
Import [http://kernelnewbies.org/status/latest.html Kernelnewbies status] list
Import relevant data from [http://www.codemonkey.org.uk/post-halloween-2.5.txt davej's post halloween document]
- Keep track of what gets changed