I have had some guys do this against me. Here are my thoughts.
1. Why would anyone really want to do this? Tennis is not all about winning. To me, this is junk balling and it really doesn't help the guy who is doing it in the long run.
2. The last thing that you can do, if you are on the receiving end of this, is to try to hit a spectacular passing shot and miss. It is really easy to deal with this. You can either hit a topspin lob or roll the ball cross court, and wait for the the next ball to punish. I really get a kick out of watching my opponent turning back and chasing my topspin lob after hitting one of these junkers and trying to sneak in. After a couple of these, they will slow themselves expecting a lob, and that is when I roll the ball low cross court, and I usually have a sitter.
My point is, unless your opponent sucks at lob or passing shot, this moonball thing won't work well in the course of the match or the next time you play him. I will give you that it may surprize your opponent on the first or second try and you may get a cheap point, if they panic.