Do you know which database drivers default to AutoCommit=0? I can't think of any off the top of my head, but I would like to know which ones default to AutoCommit off, if only, because the DBI docs say that it defaults to AutoCommit on:

The "AutoCommit" and "PrintError" attributes for each connection default to "on". (See "AutoCommit" and "PrintError" for more infor- mation.) However, it is strongly recommended that you explicitly define "AutoCommit" rather than rely on the default. Future ver- sions of the DBI may issue a warning if "AutoCommit" is not explic- itly defined.

And later goes on to say that the driver should default to AutoCommit on:

Drivers should always default to "AutoCommit" mode (an unfortunate choice largely forced on the DBI by ODBC and JDBC convention