Domain object oriented packing vs. tier oriented packing

The newest sample, PetCare, for the 3.0 version, comes with a new packing method: domain object oriented instead of the tier oriented packing as what we have seen before. I can see the motivation behind this approach: modularization so that an application may take advantage of OSGI in the future.

I am wondering how to use this approach properly for an interconnected system. Take an online shop for example, the business domain objects: category, shop, product, order, order item etc. have a tight connection. What are the rules of laying out packings? Is it based on what repositories will be involved on the service tier?

Any thoughts?

I realize this post is old, but I haven't been able to find any other posts regarding this via the search mechanism, so forgive me for bringing it back from the dead.

I am fairly new to Java and brand new to Spring, so for me this is a tough call. Can anyone outline the pros/cons of organizing a project one way vs the other?

In my previous experience with other languages and frameworks, things were organized by tier rather than domain. I'm having a hard time figuring out what is best practice for Spring 3 and what the advantage might be of domain vs tier packaging.

Any feedback would be greatly appreciated!