I think it was on this board where I read someone say that Bosch as a brand is not the problem, but you might want to look for the country of origin on the packaging.

In one or two accounts where someone was dissatisfied with Bosch plugs, and they identified the country of origin, it was China or India. This is just hearsay from my fading memories, and may not have come from a reliable source in the first place, so I pass it along just as a rumor that merits some data collection, not a statement of a known problem.

I use Denso and NGK, but it would be helpful if Bosch users would make note of the country of origin and report back if they detect a pattern.