Not that we have any plans to move from our official Blackboard system, but we always have kept an eye on other systems and have run test implementations of Moodle and Sakai. Moodle is also used for courses that span multiple institutions or other work that doesn't meet with Blackboard licensing requirements (ie with external organisations).
Canvas is very new and it may well get a good real world testing in Utah (where the company is based) where it has been adopted as the state-wide LMS. It has as you might expect of a new entity very basic features (and certainly nowhere near the capabilities of Blackboard in terms of assessment for example, etc), but if it can grow via Open Source, things will no doubt improve, though it does need progammers with some penchant for Ruby (Google it if this makes no sense!).
Anyway, you too can have a free course set up on their website and see what you think.