Some time ago, the Debian Developers decided to include Mono in the default Debian installation. This move was controversial, and provoked a discussion. After considering the different opinions, I decided to voice mine. More here
The overall effect on the other distros is hard to predict. On one hand, they will get some of the users that switch away from Debian. On the other hand, they will lose some users that will be scared by the wave of action against Debian, and will assume that no Linux user is safe. The other distros will surely try to counter this false assumption, but one must not forget that there are very strong IT players who are well-connected in the media, have enormous marketing budgets and are interested into strengthening it. So, my guess is that the other distros will lose more than they will get.