Just thinking about this problem the other day:

let’s say I retweet an interesting message from a twitter user just because I find it interesting and want to share it with my followers. Many people tend to send a “thank you” tweet because of this. While it is fair and I can’t but appreciate that, those “thank you” add noise to the already noisy twitter stream and can be source of distraction. Those “thank you” get my attention since I see there are new “@” to check but don’t really add much value to me.

Three Ways To Thank People for A Retweet | LucaFiligheddu.com#tb

I have often resorted to sending a direct message,  or retweeting without using the hashtag,  so I don’t clog up the stream for those watching that tag.  With so much retweeting going on,  it seems to me to be a worthy concern.