funny? Don't see anything funny here. Ah people don't know when it's appropriate and when it's inappropriate to send an emoticon. Yes, these are called emoticons, not smiley faces or something other.
I used emotes in an email to investors
I usually wait until the person I'm chatting with uses smileys too, then I chime in. The friendly ":)" can go a long way of conveying the right intent
This response is uncalled for, but I also think smileys do not belong in formal conversations. Its not only about professionalism, but also about class. E.g. you do not wear slippers to the casino.
making mountains out of molehills
It depends on the company and what are you trying to do, i think.
No no, it's emoji that aren't professional
This is just being an asshoe.
I work as a tech recruiter and i LITERALLY have my grey parrot on the 1º interviews with candidates (or jobs for me =) )