You're right, the logging subsystem still needs work before 1.0. We're using the RC label to indicate that we don't plan on breaking APIs and file formats in any major way between now and 1.0, so toolmakers and integrators can start locking down their schedule, and trust that their tools won't be deprecated in a couple months.

If it were entirely up to me I would never call it 1.0, because part of me wants it to be flawless before anybody uses it in production. But it's not up to me - a lot of people are already using Docker in production, and there are many organizations already in process of offering commercial support and services for it. Clearly they consider Docker acceptable for their needs at some level - and at some point we'll need to acknowledge that by releasing 1.0, no matter how flawed I find it to be. The improvements won't stop at 1.0 :)