No harm done - just interesting. I recently installed all-new Atlas track on my main loop (141 feet). Here is a picture of the center rollers on my Lionel Atlantic (from the latest series of offerings - '11 or '12 catalog, can't remember which) after just 20 minutes of "hard" running (pulling 13 scale reefers and a caboose at about a scale 70 mph) on that new track.
After about 15 minutes it started acting up and by 20 minutes it was really running rough. No wonder. The crude build up is very three dimensional on two of the center pickups. What I found interesting is: counting the loco, there are four center pickups. The leading one of the four (toward the front of the loco) had almost no crud on it, the next (rearmost of the two on the loco) had just a bit of crud on it, the third (leading pickup or the two on the tender) had a good deal, and the last (rearmost on the tender) had by far the most crud on it. I would have expected the other way around.
BTW - several people recommended I remove the blackening on the top of the middle rail to get better connectivity, but I noticed that all my conventional locos, even the newest like this Atlantic, seemed to have no problem with the blackened rail although some of my Legacy locos (running in conventional - that is all I run) didn't like it all. Anyway, I was going to Brightboy the blackening off the top of the center rail this weekend, but now I think I'll do it this afternoon!