The interesting thing in our case was that we had done a full-power run up with no problems, when the smoke started part way down the runway. I have no idea why it did not start during the run-up. It was one of those things where I was able to look around and see it after the engineers started shouting, because I was PNF, but by then we were probably too close to V1 for the PF to have managed a nice, tidy abort, even if I had been able to tell him what the problem was.
This was a Dornier 328Jet, which has one bleed and pack for the flight deck, and another bleed and pack for the cabin. The smoke only came out in the cabin, but really pouring out, just like stage smoke.
I don't know even know what it smelled like because I had my mask on just after I saw the smoke start. I shut off the bleed for the cabin pack, when the smoke stopped coming out fairly quickly, but still lingered. Then I swapped to PF so that the Captain could put on his mask; after that we swapped back again. If that had been a problem with the other side then it might have been a different story, with too much smoke in the cockpit to see what we were doing. The long-term effects of bleed air contamination would not have been much of a problem then!