It would be nice to have Spring.NET integrated with db4o.
I have implemented basic integration here :
http://samokk.is-a-geek.com/Projects/Spring.Net/db4o.tar.gz

Nothing has been tested yet.
 I'll post updates to the same address.

The current version supports :
- Db4o Platform Transaction Manager :
- Db4o Template, that supports both ICallback and delegate method.
- Db4oUtils, that provides utilities to create / dispose connections
- IDb4oDataSource / BasicDb4oDataSource : the exact same thing as a Java JDBC DataSource (Abstract Factory), but for Db4o. BasicDb4oDataSource delegate connection creation to 4 concrete IDb4oConnectionParameters :
* FileDb4oConnectionParameters : Direct file access
* MemoryDb4oConnectionParameters : In-memory database
* EmbeddedClientDb4oConnectionParameters : client to an embedded server
* RemoteClientDb4oConnectionParameters : client to a remote server

These classes work with the Spring.Data classes I found in the sandbox. Do not hesitate to add them to CVS, they are licensed under whatever-license suits you (Apache, BSD, LGPL, whatever)