oh yeah, number 3. needs to also not say there are shared files if it is patently obvious that the client is unable to successfully upload.

This will require some extra protocol work, I think, to really get it going, or something (I don't know enough!) but basically, there should be a query 'please test my upload ability'

Send that query to another client and the client requests some file from you (doesn't have to be a real file, could be some special filename like 'gnutellatestYYYYMMDDHHMMSS' that you told it you had, but actually you produce the test data automatically)

If you try a given number of clients (say 10) which say they support this protocol, and you don't even upload 10 k to them, then you don't go telling the whole world about your 5Tb of unique mp3s (which no one can successfully get because your sysadmin long ago blocked all incoming queries).