Hello,
I have using roundcube for long time. It's very helpful. Thank you!
To contribute the project, I just published a little python script that merges users/identities/contacts/contactgroups into one database handling with id's.
The project is hosted in Github:
http://github.com/nitidum/roundcube_merge_databasesPlease feel free to use and contribute it.
Thanks
Jordi Llonch