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The IMS drives the chains (2) which powers the camshafts (4). The bearing can fail outright, as mentioned, metal bits in the lube circuit, failed timing, etc.
But, it can also fail progressively allowing some flex to the shaft and it's chain sprockets. This flex imparts inconsistent tension on the chains which can then slip a few teeth on the sprockets. This throws off the mechanical timing creating poor running and/or allowing the valves on this 'interference' engine to 'shake hands' with the pistons and it's "Sayonara Motorsan!!"
The funny part is, this IMS issue started after Porsche redesigned the system after '02 to eliminate supposed vibration issues (and IMHO, make way for Variocam Plus). IMS is extremely uncommon on the earlier models, which are more prone to RMS failure due to their early generation seals.
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