Jim H
Yeah, your earnings are a function of how many total plays there were that day on mp3.com. For example, if I get 45 plays on a Sunday, I will usually make more money than if I get 45 plays on a Monday. There's more traffic during the week. A lot of people probably play their web rings and such while they are at work, therefore there are usually more plays site wide on the weekdays. Your other example where 6 plays equaled 4 cents, well, you now only need 3 'unique' hits per day to make money(you use to need 15), what probably happened in this case was that someone may have listened to a song more than once, maybe because they liked it or something, therefore the repeat plays got no playback credit.
Your payback also is affected by who plays your songs. If I deflect listeners to my site that have never been there before or havent been there in a while, I seem to make much more than when I don't. Other days, my hits are probably coming in large part from the stations I'm on. For example the artist that created the station may play his own station several times a week. This seems to discount to some extent, his hits on my site but the good thing about that is it's an inherent way to reduce some of the effectiveness of 'gaming the system' for example, stations that were set up strictly for pay4play where the artists may informally agree to play each others music.
Mp3.com has vowed to crack down on this and have suspended several artists from payback eligibility since there announcement to crack down.
Ray J