Okay. Got the car back from the dealer. Injectors tested okay. Everything else tested okay. Dealer tells me that a short puff of smoke is normal. Unfortunately, it was a windy day and if the technician drove the car to see the smoke for himself he would not have been able to create the kind to cloud I can generate on a calm day. Oh well.

btw, the air filter was changed recently, and also checked by the dealer, so that was not the problem. Perhaps it was low quality fuel (darn you, Exxon!). Perhaps I will try a cetane booster. Perhaps I am just not that concerned any more.

So, even though it did not seem to be the consensus of the people who commented on this thread, I think the final posting might have the right idea. I like the car. Occasional smoke aside it runs great. The glow plug might have been a fluke. I might just be too obsessive and fastidious.

I am going to stop worrying and enjoy the ride. Thanks for the advice all around.