One thing I did find when doing my 3D game, is that, whilst accelerator values were being returned when the device was vertical (both in portrait and landscape mode), for some reason my shape never moved until the device was horizontal and then tilted... Both horizontal and vertical values were more or less in the same range, so I dont know whether its a bug or whether it needs a calibration routine...
Must be internal then. I'm not doing anything fancy other than calling the function to get hte acc-values.