I have my contacts sync'd with Google.
Where is the contact data stored on my PC and in what fform is it kept?

Locally it's cached in Akonadi database (depending on your configuration, it can be a MySQL or a PostgreSQL database). As a user, you should not be concerned about how and where the items are cached though. The only real storage is still on Google servers and Akonadi only makes sure that every change you made locally is also written there.

Thank you - that's very helpful.
I'd like to have a read only access so the cache you mention would be usefull.
My application uses mysql (i'm prepared to try postgres though).
How can I determine which db type is used and any hints as to how to access it?

You find it in "System Settings" -> "Akonadi Configuration" -> "Akonadi Server Configuration"

However you should never access the database directly (the scheme can change any time, you could corrupt your data), but use available client classes instead [0].

To get Google contacts, you would run Akonadi::CollectionFetchJob() to fetch all collections, then find the "google" one and run Akonadi::ItemFetchJob() to retrieve all contacts within the given collection. Much easier then and safer then digging into the database directly

[0] http://ap.kde.org/4.x-api/kdepimlibs-ap ... index.html

Thank you very much - I now have some interesting stuff to do!