I've said it before and I'm sure I'll say it again, cleaning bottles is the worst part of my brewing process. As much as people condemn bottling in favor of kegging I've always liked aspects of bottling (it's cheap, they're portable, the bottling itself is fairly straightforward and easy) but hated one aspect: cleaning bottles.
While part of my reason for cleaning bottles is to get the labels off the more important, time consuming and frustrating part is cleaning the interior which can have black mold and beer dregs stuck to the bottom. It usually takes me around 4 hours of letting them soak in a an oxiclean/hot water bath before 1-2 minutes per bottle of scrubbing before they get to my liking. For today's bottle cleaning session of 150+ bottles that means approximately 4 hours of active bottle cleaning time.
I might just buy new bottles from now on whenever I or others don't wash them out after use to avoid the mold.