How do I create individual anonymous FTP sites for my users?

There are two methods of accomplishing this (possibly more). First, you can create a directory structure inside your anonymous FTP root directory, creating a single directory for each user and setting ownership/permissions as appropriate. Then, either create a symlink from each user's home directory into the FTP site, or instruct your users on how to access their directory.

The alternate method (and more versatile) of accomplishing per-user anonymous FTP is to use AnonymousGroup in combination with the DefaultRoot directory. You'll probably want to do this inside a <VirtualHost>, otherwise none of your users will be able to access your system without being stuck inside their per-user FTP site. Additionally, you'll want to use a deferred <Directory> block to carefully limit outside access to each user's site.

Create a new unix group on your system named `anonftp'. Please each user who will have per-user anonymous FTP in this group. Create an `anon-ftp' and `anon-ftp/incoming' directory in each user's home directory. Modify your /etc/proftpd.conf file to look something like this (you'll probably want to customize this to your needs):

 <VirtualHost my.per-user.virtual.host.address>
 
 # the next line limits all logins to this virtual host, so that only
 anonftp users can connect
 
 <Limit LOGIN>
 DenyGroup !anonftp
 </Limit>
 
 # limit access to each user's anon-ftp directory, we want read-only
 except on incoming
 
 <Directory ~/anon-ftp>
 
 <Limit WRITE>
 DenyAll
 </Limit>
 
 </Directory>
 
 # permit stor access to each user's anon-ftp/incoming directory,
 but deny everything else
 
 <Directory ~/anon-ftp/incoming>
 
 <Limit STOR>
 AllowAll
 </Limit>
 <Limit READ WRITE>
 DenyAll
 </Limit>
 
 </Directory>
 
 # provide a default root for all logins to this virtual host.
 DefaultRoot ~/anon-ftp
 # Finally, force all logins to be anonymous for the anonftp group
 AnonymousGroup anonftp
 
 </VirtualHost>