Apple has a similar problem in some ways to what Windows had: Windows developed as a GUI layer on top of DOS. DOS and early Windows were single user operating s

Apple has a similar problem in some ways to what Windows had: Windows developed as a GUI layer on top of DOS. DOS and early Windows were single user operating systems. All the multi-user stuff that has come to Windows since has felt tacked on. *nix on the other hand was built from the ground up as a multi-user OS. The iPad is less elegant in this scenario. I believe this highlights Apple's philosophy that the iPad is a personal computing device more than anything else. So rather than creating a complicated multi-user system, they opted for simplicity. On a side note: your calendar and mail problem can probably be solved by using restrictions to put passwords on those apps, which you should probably have anyway if the content is sensitive.