Originally, this thread noted that according to Jake Raby, in essence, operating at low rpms caused IMS failures (or increased the risk of failure).
So far as lugging the engine, there is a definite definition. The British use the term 'Labouring' in the US, it's 'Lugging'.
It means that the rpms have been allowed to fall out of the powerband of the engine for a particular load/selected gear. You are slowly stalling the engine.
An example would be having the transmission in a higher gear than the road speed or load requires, such as not downshifting when going uphill.
When this happens, things heat up very quickly internally and the engine will detonate or ping. This leads to shockwaves in the reciprocating parts (rods, pistons) and the crankshaft, and cause piston slap, scoring of cylinder walls, bearing wear, excess loads on timing gear (chains, belts, gears, or in this case - the intermediate shaft).
In concert with this, because the rpms are low, coolant and oil are not flowing at their optimal rates or pressures further compounding the effects and/or damage.
I agree that theoretically, running the at higher rpms can create more wear. I say theoretically because these higher rpms also allow greater flow and pressures for the oil and coolant which can now better protect against wear.
But, the point here was the IMS. And it is at low rpms that the oil pressure and flow are at such a low point that the inherent weakness of this part is more readily realized - it fails more easily and perhaps more quickly.
Drive it 'harder' and you may take say 10-20k mi. more off the life of your bearings and such over time than if you drove at lower rpms.
I think the point Jake is making though is that by doing so, at least your car will actually reach that kind of mileage, where without it, the IMS will grenade the motor much sooner.
But, I think we need to distinguish between the early cars and the later ones when in '03 Porsche re-designed the IMS.
IMS failure in the early cars is virtually unheard of, in fact, I can't think of a single instance being reported in the pre-'00 cars (though I'm sure there must have been some).
