I initially thought this would be a rather uninteresting release, especially when we learned Xen dom0 didn't make the cut. Following the changelog line-by-line, this one still didn't seem very interesting to me. But analyzing the sum of parts, I have to consider 2.6.30 a 'golden' kernel -- certainly the best in a while.
There is solid improvement top to bottom here. A lot of the new KMS/DRM stuff from Fedora 11 has worked its way up stream. File system work is too much to mention, but highlights include relatime, writeback by default for Extfs, NILFS2, Btrfs development and more. FSCache works as advertised. Also some groundwork for NFS 4.1, which will eventually bring us pNFS.
Boot speed seems fast as ever, but I haven't taken the time to do any empirical analysis. Your results here will be hardware dependent but async initialization of certain subsystems is a welcome move in the right direction.
Basically, a solid release with a good balance of new stuff but mainly refinement of existing systems and merging of longstanding patches.
Kernel Newbies has, as usual, a great change summary: http://kernelnewbies.org/Linux_2_6_30