No, not really. But a few months ago Zynga had astronomically high numbers of people playing such games as Cityville, Farmville, and Mafia Wars and everyone was anointing Zynga as the kings of casual games. Investment started flowing in, Zynga started acquiring other companies, they were the new Facebook (but with make believe cows instead of make believe friends).
NOW the popularity of those games seems to be dropping, in some cases dramatically. In one month, Cityville dropped from 21.1 million users to 19.7. Farmville from 13.8 to 12.7. Mafia Wars from 5.5 million to 2 million
Why? They're crappy games for one thing. And after the addiction wears off, you can walk away. It seems that Zynga is really fashion-oriented, meaning the pressure is now on them to keep coming up with new games because the old ones might not be as evergreen as we thought.