**System Information**
Debian GNU/Linux Jessie (testing)
AMD Phenom II X4 850
**Blender Version**
Broken: 2.71
Worked: 2.70a2
**Short description of error**
I observe extremely slow rendering using particle system and activated motion blur.
**Exact steps for others to reproduce the error**
You can try [1]. Switch to cycles render, enable Motion Blur. Go to frame 103. Render.
Thanks,
Andrey
P.S. [1] is originating from [2]. I believe it is inspired by [3], but BlenderDiplom's version is not cycles ready.
[1] https://www.dropbox.com/s/toy8iwfp1gyr51e/Logo%20reloaded.blend
[2] http://www.youtube.com/watch?v=FB4SZCTIcuo
[3] http://blenderdiplom.com/en/tutorials/394-tutorial-dissolve-your-logo-in-blender-262.html