What we need isnt the same as a dropbox integration, that is - What we put in Google Drive should stay in Google Drive, not beeing converted to and from doc/xls-format.
It would be much much better to be able to point out a folder in Google Drive for each project, and be able to attach documents from that folder (really just links). Of course it should be possible to browse my own google drive and attach documents to the project.
Right now we use our intranet as a portal/gateway to our projects - where we per project have two links, one to google drive and one to zoho projects, teaching our users to open the project "portal" trough there.