Just like the number of followers on Twitter has become a status symbol and a commodity, the number of lists you are on is also going to become a status symbol and commodity.
You can expect services to very soon show up that will have all kinds of schemes to get someone on as many lists as possible. Paid, reciprocation, etc, etc. So, better set clear rules and limits right now, before it becomes a fire that you have to put out. Dewald