Lately, I've been looking more and more into Resin + Quercus as a technology to develop an application of mine.
The reason I started looking into it was that this application has high reporting needs, a lot of which cannot (or realistically, should not) be created in real-time. Java would offer a nice backend to queue and generate reports. Also, with Quercus I would be able to develop my data models in Hibernate, and use them "from PHP", thus effectively stretching these models across front and back-end. This same concept would also apply to any front/back-end common business logic, which could be developed in Java libraries.
Now, the downside is that whichever front-end (PHP) MVC Framework I choose (my goal was Symfony 2), it is unlikely to work without some heavy modification, if it can work at all. Quercus is a pretty close implementation of PHP, and is supposed to be compatible with PHP5.3, so namespaces and closures SHOULDN'T be a problem, but when I tried to run an existing Symfony 1.4 app, I failed miserably.
So, my question to you is, do you think the benefits of Resin + Quercus outweigh the overhead of using a not-so-perfect/stable implementation of PHP? If this were your application, and your goal was and end-product, rather than educational purposes, what would you decide?