To everyone who says that using Incognito mode or a Guest account will fix the problem: yeah, most of us already know that. The problem is, most of us (HN readers) are not the average Google user. The average Google user is more like your granny. When she borrows Uncle John's tablet, she expects it to work just as if she had borrowed his lawn mower. Lawn mowers mow lawns just fine, regardless of who owns it. Why shouldn't tablets do the same, asks the average user.<p>In addition, the problem that OP describes is only a <i>symptom</i> of a much larger paradigm shift that (a) has been happening for a while, and (b) is in the interest of many Internet services to impose upon users, too. The idea is that a computing device only has a single user at a time. Instead of logging in and out all the time, you just stay logged in indefinitely, so that identification of a device suffices to identify the owner and everything you do on your device can be attributed to you. Logout means nothing if they can still track you with extremely-difficult-to-delete "evercookies".<p>The problem is, even today, most devices are only single-user 99% of the time. Ordinary people borrow one another's laptops, tablets, and phones all the time. Because devices get lost, stolen, damaged, or out of battery all the time. Because when your best friend buys a shiny new iPad X, she lets you borrow it for a couple of hours. Desktop OS's have Guest accounts, but they are often not enabled by default, and even when enabled, it's a hassle to switch accounts. So when a service is designed on the assumption that a device only has one user at a time, it works 99% of the time, but it fails in an ugly way the other 1% of the time.<p>When a cousin borrows your brand-spanking-new Android-based LTE-enabled DSLR (I don't know if such devices exist, but why not?) to take pictures on her trip to Hawaii, you shouldn't have to worry about having inappropriate photos of her automatically uploaded to your Dropbox and stay there even after she deletes them from the camera. Ditto for your Gmail app, any other app that identifies your device with you, and any web app for PCs that work under similar assumptions. Something is suboptimal here, though I'm not sure how it might be fixed without great inconvenience.