I can't generally use built-in functions with Class::DBI because when it builds queries, it puts quotes around everything, so if I try to set the field like:

{created_on => 'NOW()'}

It will translate that to:

SET created_on = 'NOW()'

Which is a string and will error out (note the quotes). It's a severe limitation of Class::DBI, but one I don't have time to fix right now.