Meanwhile, in August 2009 "noise" was added as reason for comment flagging, and the comment flags show in the 10k tools. And Allow low-rep users to suggest edits is on its way. Hence: I don't care for this request myself anymore. An explicit
[status-declined] would be fine.
What about being able to set comments to auto-expire? Or, alternatively, set a comment to be removable by the author of the question or answer one comments on?
This way the communities would allow for some personal or funny comments (even like "Thanks") without those comments littering the sites forever. Or, when the original author is allowed to clean up, then comments that have been taken care of by editing the question or answer, could be removed.
As, by design, there's no way to send a personal message to other members, I find myself abusing the comments like some "poor man's private messaging system". I try to refrain from things like "Thank you", but sometimes I do want to point out something to someone. After a while (hours, days) I then search for those comments to remove them (hoping that no-one actually replied to them with another comment, like "Thanks, fixed it").
(I don't find this feature request very important (at all), I am quite impressed by what's been given us already, and I doubt there's a way to implement it without making things too confusing. Maybe I'm just trying too hard to keep things tidy and clean. Still, I wanted to share it, just in case someone comes up with something very clever...)