From my limited diagnostics I was able to do on my 99 740il I determined the problem I have (same symptoms as Bruce R) is faulty Vanos Adjuster Units. My car has what feels like a perfectly timed misfire/shudder most noticable around 40 or 45 when the transmission is in overdrive and torque converter locked up. The harder you accelerate the harder it pounds and makes that grinding noise. I had noticed on my road trips to seattle for parts that if I shift into sport mode the shudder is gone. Though the shudder is there at higher speeds it seems to be less harsh the closer the rpms are to 2k.
My explaination is as follows. I have had a P01519, and P01522 cam adjuster codes since i bought the car. Reset them and they are back as soon as i start the car up. I diagnosed this as a vanos issue based on some of the characteristics of how the engine runs. It seems to be a little sluggish at low rpms and kicks you back in your seat above 3k. The shudder is gone over 2k which is getting closer to where the vanos system is backing off. At low rpms vanos is fully active and thus the worn out components are slipping the timing and having to be readjusted over and over. I have replaced both vanos solenoids with no change.
My old auto instructor clued me into the "logic" built into these luxury car transmissions. In the case of a large misfire or loss of engine power the transmission computer slips the torque converter clutch to keep the car from jolting. If you pay attention to the rpms you can see when the clutch releases and then locks back up. Some times going up a steep hill with the low rpms i will get a prolonged shudder where the torque converter clutch doesnt reengage because the engine is running too rough.
Now as with everyone else, I am human and I could be wrong but id be willing to wager that im right. I am a newbie to BMW and there was a sharp learning curve but I think im starting to understand some of it now. The internal camshaft adjuster unit on the m62tu is something like 600 dollars apeice so for 750 i bought myself a new engine (102k miles.) My engine has 229k miles and is ready to retire. I have the new engine on an engine stand and am waiting on some new gaskets and seals for it. As soon as I tackle the job and swap out the engine I will be back to post my results. In any case now I got 4 spare vanos solenoids. :P