I created an attachment plugin for a client which routes around the Elgg core file system entirely to allow people to attach files meant for single users. Attachments are placed in a special attachment directory and are represented as annotations on other entities (in this case a message) and so have no metadata themselves (and the same access control as the message).

I might release it eventually although it would need to be recoded because of the change in the data directory structure for Elgg 1.7.

Wow, sounds like what I need. I think it's a good work around for people who want to share files but only for certain individuals. Please make it! :D

take care.