New features in the "stable" kernel

A few things have happened in 2.6:
NUMA API
4K stacks
Non-executable stacks
NX page protection support
Laptop mode
Audit framework
CFQ disk scheduler
Netpoll interface
The kref mechanism
ia32e architecture
Generic kernel thread support
Tons of "sparse" annotations
Device mapper crypto, snapshots, and mirroring
Scheduling domains
Object-based reverse-mapping VM
...