"Borrowed games will be unavailable on even an authorized device when the lender’s library is currently in use on another computer."
Wait so basically you, the lender needs to be offline for the other person to play any game from your game library? I love it that Valve is deciding to implement something like this since its been a requested feature for a long ass time but If I understood correctly that limitation its basically the same as sharing an account while another being offline or worse, it forces you to be online and kicks the other person out.
Also, I assume this will only work for steamwork games?
After reading the official page I realized that this is a bit better than sharing an account since you never have to worry about the other person ever doing anything stupid with your account like deleting your game profiles, giving away your items or worse stealing it.
Can't wait to try this out, considering I only game about 3 days a week, I can share with a friend and try his games, hopefully without much trouble.