Looks like there is a bug: When set to "Mobile Uploads - Photos & videos via Wi-Fi only", photos won't mostly upload at all. Only 1 time it did upload photos I made, after entering a Wi-Fi. That's really sad, and makes the most important feature useless for many users. If this doesn't get fixed asap, I need to fallback to "Auto Uploader".
If you're suffering from this problem, too, please report a bug withing the app (menu button->send feedback). I'm afraid this specific bug will never be fixed otherwise.