We use virtual domains for web and also for emails. Usually there exists one shell user/group per virtual domain. It has many advantages - user can upload files with scp, php can run with different uid/gid for every virtual domain, etc. Postfix also supports different uid/gid for every virtual mailbox (virtual_uid_maps, virtual_gid_maps).
We would like to have the possibility to change uid/gid and homedir for every virtual domain.