I'm in the same boat as moondragon. Would def need an import script from PhotoPost -> Photoplog to be able to switch.
vBulletin has import scripts for tons of different forums and I bet it's a major reason why people finally decide to pay and switch. IMO it's just plain good business sense for PhotoPlog to try and lure as many potential customer as possible and that includes customers who wants to switch from Photopost.
