This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Absolutely. The patterns give you guidance on how you might allocate the existing behaviors to different modules, expose those behaviors, and manage the dependencies. My recommendation is to take a look at the patterns and imagine how you might use them to modularize an existing application. In fact, there reference implementation in Chapter 7 does exactly this. It takes an existing application that's just one large monolith and applies the patterns. The result is a highly modular architecture.
In reality, how you modularize your application is going to shift throughout development. Looking at modularity across the lifecycle, it's easier to design coarser-grained and larger module earlier in the lifecycle. Then as things stabilize, introduce finer-grained and smaller modules through a bit of refactoring.
Visit the book's website at modularity.kirkk.com where you can review all 18 patterns and download an excerpt of the book. There is also a mobile web application available that you can take with you wherever you go.