@raix, here is an implementation that works without your meteorToMongoId code. The basic idea is this: Let gridfs generate the initial ObjectID, and then store ObjectID.toString() in fileObj.copies.key. For future overwrites, reads, and removes, we then convert the fileObj.copies.key to ObjectID and use that for lookup. We can't store the ObjectID directly because Meteor seems to convert it to LocalCollection.ObjectID, which doesn't work for lookup later.

For this to work at the moment, you need to also use the `usekey` branch of `cfs-storage-adapter` that I created (see issue CollectionFS/Meteor-CollectionFS#252). If this all sounds good to you, feel free to merge `usekey` and `mongometeorid` branches into their masters.