The Linux 2.6.39-rc6 release that was made available yesterday isn't really exciting at all. As Linus says in the release announcement, "Most of the stuff here no normal user will ever really notice (like the ARM kprobes series), and most of the rest is the usual one-liner random driver stuff."
While it may be a "boring" release for most people, this won't be the last -rc before Linux 2.6.39 goes gold. Linus is expected to tag at least one more release candidate before calling this kernel ready. This kernel also doesn't yet fix the power issues that many users on a variety of hardware have been experiencing since the Linux 2.6.38 release.