Unless they are familiar with storage and where "stuff" goes, any time I look at someone's computer with more than one storage device, I usually notice everything is on the C: drive and the storage drive is completely empty.
Derailing this for a bit.
There's an easy way to solve this: move the users folder to the data drive
. Chances are most people are only comfortable with Libraries and user folder and don't touch the drives. Doing this will save everything to the data drive without them knowing any better. It also has a hidden benefit. If you need to reinstall the OS, there's no need to back anything up (well, you should, but you don't have to). When you reinstall, repeat the process.