I like magic words as a record of which podcasts I've listened to. I like looking at the list and thinking "wow! Look at all those podcast episodes I listened to."
So I'm in favor of extending the time period for those times when I am on vacation or whatever. A week seems reasonable to me.
I wouldn't want someone new to come to the podcast and rack up a bunch of PoP by listening to all the back episodes (or worse, by getting the codes from a friend). So there should definitely be a cutoff or drastic decline in PoP after a reasonable amount of time.
My vote is to make it simple and just cut it to a week for now. We've got some bigger fish to fry than implementing an algorithm for declining points over time (unless it is super easy).
Someday we'll have dynamically generated magic words inserted into the podcast that is unique to each user. Who's with me? :)





