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 shouldn't 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] (need to ask for permission?)
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
2.6.14: 2.6.13: 2.6.12: 2.6.11: 2.6.10: 2.6.9: 2.6.8: 2.6.7: 2.6.6: 2.6.5: 2.6.4: 2.6.3: 2.6.2: 2.6.1: 2.6.0: 2.6.0-test9:
[http://lwn.net/Articles/44243/ libata driver architecture] (Jeff Garzik)
2.6.0-test6:
[http://marc.theaimsgroup.com/?l=linux-kernel&m=104344596912094&w=2 32-bit dev_t] (Andries Brouwer, Al Viro)
2.6.0-test3:
[http://www.nsa.gov/selinux/index.html SELinux] (Stephen Smalley, SELinux team)
2.6.0-test1:
[http://www.linuxvirtualserver.org/ Linux Virtual Server layer] (Wensong Zhang)
2.5.75:
[http://marc.theaimsgroup.com/?l=linux-mm&m=104529418208788&w=2 Anticipatory Scheduler] (Nick Piggin, Andrew Morton)
2.5.71:
[http://marc.theaimsgroup.com/?l=linux-kernel&m=104981044405395&w=2 Switch the IDE I/O layers to taskfile](Bartlomiej Zolnierkiewicz, Alan Cox)
2.5.70:
[http://www.linux-usb.org/gadget USB gadget support] (David Brownell, Stuart Lynne, Greg Kroah-Hartman)