[Quoth]

Loan the ereader?
Any other sort of "loan" is a copy outside of your control, no matter how much you trust the person.

No issue with giving a copy of a PD book, but a "free" copyright book should be downloaded by each individual, not copied or "loaned".

I can't see how you can truly loan a digital file on it's own unless you are a real library, otherwise you can only loan the hardware it's installed on.

A fourth category is where you own the copyright. Again, I'd only loan the hardware or a paper copy and give a copy with injunction that it's only for personal use.

A fifth category is the concept of some sellers of a "family" licence, though they expect to enforce this via DRM. Again, you can't loan except you loan the hardware. A copy is a copy.