With engine management software it should adjust the detonatin, timing etc. to accomodate the lower octane fuel without causing any problems over a long period of time. Any issues that would come up would materialize in the form of engine knocking (which would be resolved by switching back to the higher octane fuel)... I really don't see it as being much of a risk or causing any damage to the engine.

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Current Cars:

2008 X5 4.8i - Blk/Saddle
2001 330Ci - Titanium/Black Sport/Premium

Past Cars:
1993 325is Blk/Blk Sport
1995 M3 Blk/Blk
1997 328iC Blk/Blk Sport/Premium
1998 M3 Silver/Black
2001 M5 /Black/Black/Sport
2005 X5 3.0i - Blk/Blk Sport/Premium