Hi, this is my first bugreport, I hope it's not too bad.

My blender version:
The splashscreen doesn't show the revision. It is a build from build.opensuse.org/home:djs_core, the version shown in my opensuse installer states "2.56.34784-101.1"

How to reproduce?
open blender, open a python console window in it, type in:
>>> import mathutils
>>> q = mathutils.Quaternion()
>>> q.rotate(mathutils.Quaternion())
Traceback (most recent call last):
File "<blender_console>", line 1, in <module>
TypeError: quaternion.rotate(value): expected a Euler, Quaternion or Matrix type, found tuple

Same result for:
>>> q.rotate(mathutils.Quaternion().to_matrix())


So it looks to me like the function plain doesn't work. Having looked at http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Scripting I didn't see any mention of it (or of quaternions), and http://www.blender.org/documentation/250PythonDoc/contents.html cites it as unlikely to change.