As you probably know, I work on KOffice. Have been doing that since before the first release and I did most of the (flake)libs and KWord work in the sprint to the upcoming Koffice2.0 release.
A big reason for working on KOffice is that its fun! Another, at least equally big reason is that I believe KOffice is the best open source office suite for the long term. And so follows the question; What makes a successful open source project?.
If we look at what others have said on the subject we come to the conclusion that the things that count most are these 3 points;