I have found the Someday/Maybe list to be very effective for managing customers and prospects.
In a given week, I only have so many hours. So at the beginning of the week, I make sure I have next actions for the customers that I am currently working with or plan to work with this week. Everyone else goes to the Someday/Maybe list. If I find that I have more time that I thought, I go to the Someday/Maybe list and select my most promising prospects from that list and add them back into my active list.
I find that I make must more effective use of my time if I have a healthy Someday/Maybe list to work from when there are lags during the week. If I tried to work with everyone all at one, I would be overwhelmed. If I didn't have anyone ideas of who to work next with once I closed a sale with a customer, I would waste time figuring out what to do next. It's much easier to run a profitable business if you have an active pipeline going.
I've heard people say on this board before that customers do not belong on a Someday/Maybe list. I completely do not understand where those people are coming from. I have a hard time believing that they're in sales and they have any clue as to what it is like to generate leads in order to stay in business.
Nobody is someday/maybe when it comes to customer service issues. If a customer needs something, I take care of it right away. But as far as a prospective client goes - someone who I am not working with but would like to have as my customer if and when the opportunity presents itself, I think the Someday/Maybe list is perfect for those situations.
I find that if someone is on the S/M list, my subconscious mind works behind the scenes, and I am far more likely to spot a good opportunity when it occurs rather than afterward (when I can only kick myself).
You might argue that the Waiting For list is more appropriate, but with that you have to know what you're waiting for. You might wait for the wrong thing and then miss an opportunity for a sale. Planting a specific idea in your mind - like "waiting for customer to rause funds" puts limits on the situation, and they may end up making a decision without ever raising the funds you thought they needed because the real hang-up was getting everyone to agree on what they wanted.
So I definitely see a place for the S/M list in sales. In customer service, no. Does a hot lead go in S/M? No. But potential leads that are going away just because you don't act on them this week are perfect for the S/M list and can keep a business running consistently rather than in spurts.