WordPress announced that they we be delaying the release of 2.7 which I consider a good move.
From the WordPress Blog:
There comes a time in every WordPress release when it’s ready for the world , to come out of its cocoon and feel the light of the world on its wings for the first time.
WordPress 2.7 RC1 was a bit buggy. The popular plug-ins have not been successfully ported over from 2.6 to 2.7. Twitter Updater and Kimili are both broken. I have problems uploading images with the Admin GUI forcing me to manually edit the HTML.
That is not the developers fault though, it is mine. I did test the last beta version of 2.7 before the release candidates with no problem. For me, most of the bugs appeared with RC1.
RC2 has been released which should be more stable but for most people, just wait for stable 2.7 or test it on another test blog. It is nice and I love the features I can use so far.
Read more about the delay and RC2 here -> http://wordpress.org/development/2008/12/27-release-candidate-two/