This thread (and the other linked thread to McDonaldD’s) compelled me to register and post. As others have stated, by virtue of the power of observation and a bit of mechanical basics, one can conclude that valve stem seals are not the likely culprate to the ‘idling smoke puff of shame’. Whether you drive a BMW or an Acura or Ferrari, vacuum leaks are the devil. This does not mean that valve stem seals don’t fail, it’s just not very common. Not as common as the internet would scare someone to believe and if true would be a huge failure on BMW’s part.

I picked up a 2006 4.8is last week knowing that their was smoking after prolonged idling. However, with how well the engine pulls like a freight train (and concluding a 2,000 mile road trip from picking it up at its place for sale) I am not convinced at all that the valve stem seals are bad. Coming across this thread after five days of searching different key words and reading all the subsequent linked-threads further solidifies vacuum/oil leaks that my IS is currently experiencing. Today being the first day I have had time to take a look around the N62, I have high confidence this is the case.

Summarizing my observations:
*passenger side valve cover noise dampener has oil around the knock outs for the dipstick and CPS.
*pulling off all noise dampening covers reveal both camp position sensors are weaping oil.
*the sensor on the pass-side valve cover in front of the CPS is weaping oil
*the oil filler cap is weaping oil.
*the oil dipstick is not nesting as tight as it should be. Generally on a new motor there is a bit of a ‘pop’ noise when pulling out the dipstick.
*CCV are in good shape, however there looks to be a misalignment issue on both valve covers (not sure if this is normal). Meaning the black plastic hole does not rest equally centered/alligned to the hole below it on the heads. These two respective holes are off by about 3 mm.
*passenger side vacuum hose valve-cover-to-intake-manifold is gummed up with brown crud throughout.
*driver side vacuum hose valve-cover-to-intake-manifold is gummed up with brown crud on the intake port side.
*the bunge located above the throttle body is restricted with brown crud.
*inside of intake manifold shows signs of oil contamination. While I can still see some of the green coating, oil is in there.
*PO had the alternator replaced. I am unable to verify whether the gasket was replaced during reinstallation as discussed in the McDonaldD’s thread. This can also be another point of contention for vacuum leaks.

*Oil consumption is low and under the threshold outlined by the BMW bulletin.
*Gas mileage is around 23-24 highway and 18 city.
*Engine purrs like a kitten at idle and through out rpm range.
*Engine pulls and pulls when the gas pedal is into it.
*no weaping anywhere else around or under the engine.

I like to weigh time involved vs repair price. I’ll be starting with the cheapest solutions first basically replacing every gasket, o ring and hose in and around the vavle covers. Thanks to the OP and McDonaldD for their insighful and detailed threads. Very much appreciated.