My friends who work in the webapposphere tell me that .NET is the tool of choice for quick'n'dirty weblications, but for real work you almost always end up with Java + Oracle.
We're currently building a very large application (30-odd servers, vast amounts of data (it's GIS-based in part), web-driven front-end, etc) and the only serious toolset for this is Java of some stripe or other. We're an Oracle shop anyway, so it'd be daft not to leverage that.