Everyone I talk to who knows (knew) about it claims it was the greatest thing since sliced bread. Why did it fail? Or, if it didn't fail, who's using it now?
Check out GigaSpaces. It's a quite successful Jini/Javaspaces implementation.
I think Jini has a great model, but it is stuck with Java. Web-services is more appealing because it works with standarized protocols, even though Jini service discovery is more natural.