I know that PostgreSQL allows you to not specify some fields when connecting. When they are not specified, the behaviour is a little different, and in some cases very different:
username: if the username is not specified, the "unix" username is picked.
password: if the password is not specified, then instead of authenticating against a password, ident is used, that is, it checks to see if you are logged in to the local machine as that user... but to do that...
host: if no host is specified, a socket local connection is used (or something like that).
dbname: if no dbname is specified, a db named after the user is picked.
It would be nice if postgressqlConnect and genericConnect would allow such behaviour.