Short overview (for news sites, etc)
With 2.6.20, Linux joins the virtualization trend. This release adds two virtualization implementations: A full-virtualization implementation that uses Intel/AMD hardware virtualization capabilities called KVM (http://kvm.sourceforge.net) and a paravirtualization implementation (http://lwn.net/Articles/194543) that can be used by different hypervisors (Rusty's lguest; Xen and VMWare in the future, etc). This release also adds initial Sony Playstation 3 support, a fault injection debugging feature (http://lwn.net/Articles/209257), UDP-lite support, better per-process IO accounting, relative atime, support for using swap files for suspend users, relocatable x86 kernel support for kdump users, small microoptimizations in x86 (sleazy FPU, regparm, support for the Processor Data Area, optimizations for the Core 2 platform), a generic HID layer, DEEPNAP power savings for PPC970, lockless radix-tree readside, shared pagetables for hugetbl, ARM support for the AT91 and iop13xx processors, full NAT for nf_conntrack and many other things.
Important things (AKA: ''the cool stuff'')