If you want to share files by using the FTP method you really should rethink the protocol. There are better solutions for general P2P file sharing out there (BitTorrent, Direct Connect).
To let people browse through your files from almost anywhere you can set up a FTP server (wish there was SmartFTPServer).
Users can then connect and browse through the mounted directories.
To give a user a file via FTP you only need to make a link like this:
Anonymous access to file mysecrets.txt on path /secret
ftp://ftp.yourserver.com/secret/mysecrets.txt
You know the guy and let him do everything:
ftp://myfriend:leet@ftp.yourserver.com/ ... ecrets.txt
where "myfriend" is username and "leet" is the password.
Most browsers understand this syntax and a lot of file browsers (Nautilus and Windows Explorer via IE core) also support it by using Virtual File System techniques.