They're a good idea but... the api is, well, stupid. I haven't got one but looking at the documentation, if you want an application to do something you have to request a url to their server, and then they send the information to your nabaztag. Apparently on Christmas day last year the server went down because of all the people with new nabaztags, and they still don't have RSS feeds back up (edit: or something). You also have to pay for certain extra features I think(?).
It would probably be fairly easy for someone with good network related programming knowledge to spoof the packets, but from a recent search I made I could only find one person who was part way through an attempt.
edit: I do like the idea of an RFID reader in the new one tho