Saktoth, to answer your question, I personally haven't had any issue with idling in games however new players I've tried to introduce the game to do. When I watched this most recent replay, it appears that my friend was just watching a couple units he was making finish building. Almost immediately after his units were given to his teammate he moved his mouse again and got (almost) everything back.
Technically, I think the feature is a great idea but I guess I don't understand its need. I understand giving away units if a player disconnects but how often does a player just leave the computer in the middle of a game long enough where it causes problems for the team?
If the feature is here to stay then I hope it gets better at giving all the units back to the original player. It's not fun to see that kind of frustration in a potential new player. If posting the replay or logs or anything would help that effort then let me know.