Hypersonic is there really to get you up and running quickly. It is not recommended for production systems (unless in-memory database is really what you want).
I would recommend installing PostgreSQL for your production needs.
I would have to agree with you that Hypersonic is not very good for production systems. Although according to their website, they believe it can be :) But even for getting started, it makes more sense to have a disk-based database since that is what most people would require. I am in the process of connecting MySQL and I hope everything goes smoothly!