I agree, Christian. We are also a large enterprise using both Java and .NET, and using a Maven-based build process. The clear benefits of using NMaven are 1) use of the Archiva repository for binaries, 2) versioning capability, 3) reproducibility, and 4) consistent tooling throughout the enterprise. We have been working off the 0.14 branch, but would love to move over to the trunk as soon as the full functionality is available there.
The VS interface has proven to be very valuable to us - it makes it easy to port an existing project over to NMaven, as well as enabling users to use NMaven for builds within the IDE. There are a few items which could still be cleaned up, but the main functionality is there. The key to increasing adoption of NMaven is letting the .NET world know about the functionality that is available - I've not been able to find *any*other product that addresses versioning, reproducibility, or has even a vague concept of a binary repository.
