Steps to replicate:
1. Import a BVH motion cap or other skeletal animation.
2. Export as Collada
3. Import the Collada file.
Nothing will import. After tracing the code, it appears that Documentimporter expects armatures to be attaches to skins. (i.e. functions like get_armature_for_joint all assume there are skins being imported as well). In the case of importing a BVH file, there will never be a skin.
Not a show stopper, but for those people that have their animations stored as DAE files, it might be confusing.
Currently not too much time to work on this, so I'm moving this to our todo list on the wiki: http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Simple_Todos#COLLADA
Anyone who wants to help out still can provide patches!
Thanks for reporting.
Reopening to be able to assign to Jeroen.
Jeroen, if you start looking into this at some point, I think currently a skin controller is a must for armature animations to work. Probably doable to fix though, but this might be longer term work. Nonetheless, reopened :)
Marking as todo, as this will require long term work. Possibly a GSoC 2011 candidate will work on this (proposing full COLLADA animation support in Blender). Can reopen when this is being worked on, either as the GSoC or in other form.