Check it out at lkml.org or this summary at kernelnewbies.org

Summary: 2.6.27 add a new filesystem (UBIFS) optimized for “pure” flash-based storage devices, the page-cache is now lockless, much improved Direct I/O scalability and performance, delayed allocation for ext4, multiqueue networking, an alternative hibernation implementation based on kexec/kdump, data integrity support in the block layer for devices that support it, a simple tracer called ftrace, a mmio tracer, sysprof support, extraction of all the in-kernel’s firmware to /lib/firmware, XEN support for saving/restorig VMs, improved video camera support, support for the Intel wireless 5000 series and RTL8187B network cards, a new ath9k driver for the Atheros AR5008 and AR9001 family of chipsets, more new drivers, improved support for others and many other improvements and fixes.

Good Stuff.