Meetup uses it to some extent. I don't know how much, but I'm told by some of the programmers I know. I think it was Andrew who gave a Jython talk at Meetup HQ a few months back.
Jython is a great way to leverage the huge the amount of libraries and infrastructure available on the JVM. It also lets you reuse what you might already have, which might allow you to (covertly?) transition languages. I use it regularly.
If you're not already entrenched in the Java world, you probably don't need it. I use it because my clients are comfortable deploying WARs, EARs, JARs, SARs, etc. Oracle and IBM sell a full stack, so there's never any scrutiny.
Technologically, you might want it. Despite the tendency to ignore them, Java has a lot of superior tech that comes in handy. You'll get real threads, connection pooling, distributed transactions, fantastic async I/O libraries; Jython inherits all of this. If you need this, it's available. You don't have to roll your own. (You will have to learn it, though, and I think that's what really drives NIHS...) Understand that Jython does come with a performance penalty on some tasks, but pays dividends on others. You can also spot tune with pure Java to some extent.
So it's really a strategic thing. If you're selling into orgs that have established practices, or if you need really serious throughput, Jython will probably be a good choice. If you're building a web app that you run on your own infrastructure and you've already chosen Python and Django, you're probably better off without the extra layer.
