According to this wikipedia page:
As of August 2011, Canonical is requesting contributions be licenced under a Harmony Contribution Licence Agreement, rather than the copyright being assigned to Canonical.
This would appear to put contributors in a better position, being able to maintain the copyright of their contributions. Are there still any drawbacks? Does the contributor lose any rights with the Harmony agreement that they would have kept when contributing to a project without a Contributor License Agreement?