From The Death of NUnit - Will it be Ice?, written by Charlie Poole, one of the NUnit developers:

Our mistake seems to be keeping it in the source and forgetting the importance of frequent releases. We’re working on that and I hope to get a new iteration release out in the next week or so, if only to keep from having to deal with bug reports on problems that are already fixed!

I hope they get themselves back on track soon. I know how difficult it can be to keep up the momentum of open source software releases and it's essential that there seen to be life in the project.