Guys, from your practical experience, what is the lifetime on spark plugs?

And between BMW or OEM which ones have you changed and what is your experience? (I know this is debatable topic).....

I replaced my spark plugs at 90.000 miles. I used NGK BKR6EQUP (about $7 at AutoZone).

As you can see on the diagram you can also use BOSCH FGR7DQP

http://realoem.com/bmw/showparts.do?...04&hg=12&fg=05

I change em every 60k or so, simply because its relatively inexpensive,.

I believe BMW says 100K miles. However, there are those that changed them at around 60K and noticed an improved difference.

50K, I change them every 30K though because they're free.

What do you mean by "they are free" ?

I assume you are talking about having them changed while under the maintenance warranty, but will the dealer just change them if you want?

After having a problem with an ignition coil being shot and misfiring, my Indy changed out my spark plugs. 72K miles.