Those of us lucky enough to have an iPhone 4s have to keep iCloud as our sync method with 2Do if we want to keep the amazing ability to add tasks with Siri, so the new Dropbox sync option isn't useful for us, as far as I can tell.
BUT, it would be WONDERFUL if the backup options could be changed to allow us to use Dropbox as an automatic backup system. We would enter our dropbox account, and set the options as to how often to back up to dropbox (launch or exit, or maybe options like once a day or once a week). The reason it would be so valuable is that the iCloud synching does not do a full backup of the 2do settings, calendar colours, setup up etc. And currently the only way to have secure full backups on off of the iOS device is to remember to manually email the backup file to ourselves.
Anyway, love 2do, whether this happens or not!