Enterprise Library is an overkill. It is too complex and inflexible. So we don't use.
In our projects (including those that target distributed computation scenarios over Windows Azure) we use Lokad Shared Libraries as a lightweight replacement. It plugs to log4net for logging, Autofac IoC for configuration, provides custom business rules, validation and exception handling (with reliability) application blocks, while packing all the required assemblies in a few dll files.
