Re: Communication Issues between young and elder, alike!
I use them in a limited way, to reinforce something I'm saying, so I might write "Thank you, that helps :) "
I don't rely on what are, after all, nothing more than a grouping of punctuation marks alone to communicate the inflexion of my voice or my facial expression, so I wouldn't use them in an attempt to turn a sarcastic comment into a light-hearted one, unless I knew the person I was addressing very, very well - and I don't know anybody on here sufficiently.
When they are used in that way, I find it a bit arrogant (for want of a better word) because the writer is expecting the reader to make the effort to understand what s/he means, whereas I think the onus is on the writer to make him/herself clear. Having a joke and a laugh can often be done far better orally than in writing. My personal rule of thumb: if it reads snidey, sarky or mean without the emoticon, re-write it until it doesn't.
Edited to answer your last question: yes it does matter, by and large, if you could have said it in a way that wasn't hurtful. The only exception that I can think of off the top of my head is if the other person took offence because they were determined to do so when nobody else would have.
Thinly veiled tigress
Ladies and gentlemen, I've suffered for my art. Now it's your turn (Neil Innes)