Flex completely fails at the printing part since the system is unflexible, non responsive, got no easy way to spread content to pages without cutting at all the wrong places and yes, it fails to provide support for preview, too. If you are as annoyed about these short comings as I am, you might want to check this rather interessting link:

http://www.kemelyon.com/flexreport/

Flex Report is a open source demo about how some of the above mentioned issues can be solved and brings support for generating PDF-Files, too. It’s not perfect and the author suggests to only use it for non critical applications but it clearly is a step forward compared to the trash that Adobe delivers with Flex 3.