I'm a LotusScript man too for the most part. I just use Java when it's the best/only choice.
In this current case I'm doing some e-commerce stuff and need to interface Domino with a 3rd party "payment gateway" daemon running on the server. To process a transaction the Java agent opens a socket on port 5000 to the other software and sends some XML to it. The Java then needs to process the returned XML. Java seems the obvious choice as soon as XML and sockets came in to it.