I find myself using Java as soon as there is a back-end-only application - scheduled agents, that kind of thing.
Apart from obvious cases where Java is the only possibilty (network, complex regexes) I enjoy the superior IDE and the possibility to do Test Based Development thanks to the awesome JUnit. I tried for a while to use something similar with Lotusscript but found it to be too much of a hassle.
Java is good in that it forces me to write OO, but I find it annoyingly verbose Button button = new Button(), anyone? and some aspects just make me cringe - the whole int/Integer/autoboxing nonsense just seems soooo unnecessary, and honestly I haven't really had the use to do more than simple, one-level inheritance (i.e. genericPerson vs HappyPerson, SadPerson, etc)
Arguably, as well, I think the quality onus we have vis-a-vis clients should not be a question of language but one of professionalism: in other words, making sure that you are delivering code that will be easy to read and to maintain in the future. And, once you have accepted this as the main point, it's things like structure, architecture, and documentation which are important, not the actual language.
Many client applications I am maintaining have been done terribly sloppily, and a lot of my job is making these old things clean again - removing redundancies, making a better separation between business logic and presentation (which is a fancy way of saying 'getting rid of code squirreled away in buttons on the form', and starting using classes.
Lotusscript (especially since the new editor came in which enabled you to properly edit classes) enables you to do program almost as well and cleanly as any other OO (although the lack of extensibility of the base classes is annoying, as are the occasional holes such as not being able to create an empty NotesDocumentCollection)
I do admint to getting in a flutter when thinking that I am an expert about a dying subject and will find myself useless in a couple of years but then I always tell myself that there are a number of skills I have (which you also have) which are more important: i.e. customer skills, knowing how to structure a program, knowing how to test, those things.
For me the far bigger threat is that Notes Development is still something where a single person can develop a whole application single-handedly, and I am sweating to think of an altenative technology where that is also the case. Alternative technologies seem to me to be so complex that one can really only start with a small group of persons. In my limited visibility that certainly seems to be the case with Websphere and Sharepoint. Potentially .NET is better. I would welcome a discussion on this.