I have always thought that NIO was aimed at networking. I'm not sure that it brings much to disk I/O, perhaps @norm can help with what he uses it for.
I have found NIO to be hard to use. And when it first came out, there were serious bugs in the Windows JVM that made it impossible to use.
If you want to use it for networking, I strongly suggest you look at
Apache MINA - Index
it wraps it all, and adds very nice capabilities.