Craig Andrea of Developmentor fame, had so many problems with the Enterprise Instrumentation Framework, he dumped it for the venerable log4net library. The principle complaint? Configuration. He linked a helpful comparison on TheServerSide.Net. Being a “Smart Programmer” he was able to replace it in a day.
As I noted earlier, EIF is slated to get replaced in the Enterprise Framework.
I'm, of course, partial to the instrumentation frameworks I developed, which, of course, could sit on either one of these platforms. I developed an abstract hierarchical configuration namespace scheme, called a logspace, that could be reset at the assembly class and method level. You could also configure directly at the namespace, class and method levels. Another key feature was that the logging thresholds are configurable globally, per machine, and per logspace/namespace. That way you can slice the pie many different ways to just get the logging happening where you want. Add in traceable error codes and localizable messages (prescribed in the class library guidelines) and you've got quite a framework, I think. And in production to boot!