I'm new to the Enterprise Software world, having been mostly in either industrial or "hard problem" software. But the 3-tier application architecture we use for financial processing at our 26 state campuses (University of Wisconsin) appears to me to be typical: large numbers of individual browser (not communicating with each other) interact through a Web server farm to the Application Servers. The overall application is too large as implemented to allow the load to be accommodated, so it is divided by functional area into a farm of individual applications that do not talk directly to each other. This partitioning isn't very successful, because the users tend to do the same functional activities at the same times of day, so most of the applications sit idle while a few are at their limit. I assumed that a single database was used so that the RDBMS could ensure data consistency between all these different applications. 

But it turns out that the Oracle database can't handle that, so instead, each functional area gets its own database.  Most of the work done by the system (and most of the work of programmers like me) is to COPY data from one table to another at night when the system is otherwise quiet.

Maybe this isn't typical, but it is the architecture that Oracle and its PeopleSoft division pushes on us in their extensive training classes. And it appears to be the architecture discussed in the higher education IT conferences and Web sites in the U.S.