I print a lot of big flat floored prints and fought the curling issue too.
Once I started adding helper disks, the problem went away.
http://www.makerbot.com/blog/2013/04...-helper-discs/

Now, the latest MakerWare no longer has the helper disks as an option. However, there are lots floating around Thingivers.
I add mine to my Solidworks models before exporting them.