I regret to report a negative user experience; even allowing for the early phase of development.
After reading the posts here, I thought I'd give it spin. I read through the nxtforum posts, d/l'd the latest client, edited the conf file, fired up the testnet version and, well, ... that's about it really.
I was unable to find any instructions on how to obtain testnet NXT and, as all functionality is protected by a blanket 1NXT paywall, there's no way even to begin exploring the features, so I shut it down.
(The Java source has vanished, btw.)
Cheers
Graham