How reliable is checking cam timing in determining the IMS bearing condition? Do any shops do this during an inspection or only upon request? I'll be getting my new Boxster inspected in the next few months (if I ever find the right car) so its an interesting tool. I would expect that the wear in the bearing would have to be severe to detect a cam timing issues.

Minimally useful, as the bearing would have to already be in dire trouble before excessive play causes the deviation values to start jumping around. We have seen it a few times, and unfortunately is a lot like trying to catch a photo of a plane crashing; by the time you see it, it is already too late. On the cars we saw it happen, pulling the sump showed tons of metal already circulating in the oil, and engine's that either needed a full rebuild or replacement.

As for doing during a PPI; yes, we do it on everyone we do.

Make sure the engine is hot before taking these readings.