The case for functional decomposition

Hi all,

I'm a big fan of / and have been looking in my current development to decompose my application along functional boundaries as a route to being able to scale out the server side, specifically the database layer. The problem comes when there are links between the data in different components, ie one component holds all the user data, but another component needs to reference a user as being an owner of some piece of data. I'm currently doing this by holding the primary key information for each side of the the link (as you would if they all lived in a single database), but this link table needs to exist in both components to allow lookups to be done in either direction, ie 'get the things a specific user owns' and 'get the owners of this specific thing' would each use different components. The alternative to this would be to store the link data in only one of the components, but then the reverse lookups would require 2 calls instead of just one.

My question is this, is the duplication of these link tables some kind of code smell I should be avoiding or is this just the way things go when you split your app along functional lines like this?
Is this sort of approach really applicable to anyone other than the ebays of this world? should the rest of us just keep putting more functionality into the same back end?