This is just a quick reflection on normative behaviour and a short personal declaration. I don't thank people for passing along what I have to say, and, while I don't specifically hold it against others when they do so, I do question their motivation. And I have unfollowed people for doing it excessively.
I don't use Twitter for strictly promotional purpose, and if you do, more power to you, especially if you are promoting a product or service I actually use. But I wonder, what is actually happening when you publically thank me for passing along your message? Well, yes, I am getting the thank you, and there is some reciprocation, if one or more of your subscribers decides to add me to to their subscription lists, but this is not likely, particularly if you thank a number of people in a single tweet.
Basically, what I understand when somebody thanks me for passing along a message is "thank you, please do it again" - which is all fine and good, but to be honest, if you were to come out and ask me to "plz RT" or whatever, I would be less likely to do so, and the same goes for a lot of the "thx 4 RT" I see - it makes me feel like I'm being played. So please don't bother.
If you disagree with this belief, let me know. I'm not a rude person, I thank people all the time for all sorts of things. But I'm not going to thank someone for carrying on a conversation with me.