Linux 2.6.38 has not be released. Please be patient
Summary:
1. Prominent features (the cool stuff)
1.1. Wait until the release
2. Drivers and architectures
All the driver and architecture-specific changes can be found in the [http://kernelnewbies.org/Linux_2_6_38-DriversArch Linux_2_6_37-DriversArch page]
3. Core
4. CPU scheduler
5. Memory management
6. File systems
EXT4
7. Networking
8. Block
9. Crypto
10. Virtualization
11. Security