I had some colleagues on board...here's the story, third hand. There was a burning smell on board, which caused the diversion to RNO. (That's why they didn't keep going to SLC as one poster questioned. Ref: SR 111 accident...if there's a chance A/C is on fire, get it down now.) The cause was described as a circuit board...don't know where. The stop in DEN was because the FO went illegal in terms of flight time, so they had to get a new FO. Apparently they reached BWI at about 3 AM...