I usually use this (note the 'database:host' form) even for local connection :

$dbh=DBI->connect('dbi:mysql:database:host','root','');

From the Mysql documentation :

ERROR: Protocol mismatch. Server Version = 10 Client Version = 9
The new Perl DBI/DBD interface also supports the old mysqlperl interface.
The only change you have to make if you use mysqlperl is to change the arguments to the connect() function.
The new arguments are: host, database, user, password (the user and password arguments have changed places).
See section 19.5.2 The DBI interface.

"Trying to be a SMART lamer" (thanx to Merlyn ;-)