Does it matter which way the camera is orientated for the sensor cleaning to work?

With the advent of sensor cleaning in newer bodies - does it matter which way up you hold the camera whilst it is cleaning? I understand that the sensor cleaning works by vibrating the sensor to knock the dust off, to stick to a "very sticky bit" - but are these very sticky bits all around, or only below the frame in landscape orientation?

Answer

This article on Pixinfo talks about a test that they have made between for cameras with sensor cleaning systems. According to that, the camera has to be upright for the sensor cleaning to be effective.

However, the test also suggests that for some cameras it doesn't matter much, because the sensor cleaning hardly works at all.