People may also be interested in Ozzie Gooen's discussion document on the Advantages and Disadvantages of a Monolith Application. I'm conscious of the disadvantages, and am a believer in decentralisation.

As Niel Bowerman commented there, profiles bases sometime do evolve into monoliths. The ever-growing list of things you can do on Facebook is an example, although that's partly because Facebook is a platform for independent applications; in the same way, people can build independent applications either on top of the Profiles or leveraging them somewhere else, through .impact.