ABC's Dancing With The Stars once again trounced every other show on Monday night as a 90-minute performance edition attracted 18.80 million viewers. The show increased viewers in every half hour, capturing 17.22 million viewers in the 8 00 p.m. half hour; 18.99 million in the 8 30 half hour; and capping the evening with 20.20 million in the final half hour. But viewers abandoned the network in droves once Dancing danced off. Romantically Challenged, which followed Dancing , dropped 57 percent to 8.69 million viewers. Meanwhile, CBS's comedy shows, particularly between 8 00 p.m. and 9 00 p.m., showed significant ratings erosion of their own. How I Met Your Mother and Rules of Engagement averaged just 7.67 million viewers, down from 8.17 million a week ago. Two and a Half Men attracted 13.17 million at 9 00 p.m., down from 13.75 million last week. But The Big Bang Theory, which followed, rose to 14.75 million from 13.58 million last week. Most worrisome for the network may have been the continued decline of CSI Miami at 10 00 p.m., which drew 10.56 million viewers, down from the previous week's 11.10 million. The procedural drama has been shedding viewers almost on a weekly basis.