CNN lost an average of 179,000 adults 18-49 viewers in primetime in 2009 vs. 2008, the most of any cable network for the year. Lifetime, MSNBC, Comedy Channel and TBS rounded out the top 5 losers in that primetime demographic. The losses for the news networks aren't surprising considering the 2008 election boost, however Fox News' losses were tiny by comparison. TBS' losses were likely due in part to the fact they had the highly rated baseball ALCS in 2008 vs. the not as well rated NLCS in 2009. As far as Lifetime and Comedy Channel, your guess is as good as mine.
Cable Networks, 2009 vs. 2008 Adults 18-49 audience losers.
Primetime, Monday-Sunday, 8-11pm, Adults 18-49 (000s)
There are many target age/gender demographic targets for different cable networks and adults 18-49 is just one of the important ones (for example, news networks target adults 25-54). Likewise, total day ratings are relatively more important for some cable networks, like those targeting younger viewers, than primetime.