I've only done a few and usually it's when I have sufficient reason to do it (like I forgot to do all my homework ). I can't do more than one a week, but I try to keep it to one every 2 weeks so I don't overstress myself.
2 Chinese songs and 4 English songs. They're good, but out of the 6, I can only listen to 4 of them repeatedly since I exhausted the other two. I downloaded them a bit earlier than the other 4 and have listened to them over 100 times.