I'm glad that i have read this thread. I use this smiley also in forums but from now on i will not do it. Unless i have a good reason to do it of course.
It's not as bad a gesture as wikipedia makes it seem. It's more something teenagers do subconsiously when their parents are lecturing them to express boredom or non interest.
When adults use it (I'm 30) it seems more like using the term "whatever" and similar to a cue to change the subject, or exasperation like Charlie Brown's "Good Grief!". Would be used to get someone to stop "beating a dead horse" -restating an issue that has been thouroughly discussed over and over again...used in an attempt to change the subject.
Feel free to usie it, but be careful where and when as in the wrong timing, it could be considered quarrelsome (confrontation provoking).
J