Emoticons have actually been around since 1982, when the only video game we had involved covered wagons and dysentery and where our soda had actual calories. Those were dark times indeed. Thank god we can now simulate a pile of poop with swarming flies in our instant messaging!
There are a few situations where emoticons should never be used, such as in any professional context, e.g. resumes, job applications, cover letters, etc. There is a little bit of leeway involving work emails with coworkers, but it depends on the casualness of your office and/or clientele. The general rule of thumb to gauge emoticon appropriateness in texts or online is to mirror those you're communicating with. If you're g-chatting Tyra Banks, for instance, then by all means, type in all <3s and uppercase J's. That's how I got my guest stint as "Wind Machine Holder #3" on "America's Next Top Model."
In terms of more casual interactions, I took an informal poll because I am biased on the subject (my great-grandfather invented this emoticon <:3)~, which is either a mouse or Steve Buscemi. I can't quite remember). The consensus was to use emoticons sparingly, less so in emails, and never with those who are in positions of authority, such as school marms or your boss. You are allowed smiley/frowny faces to convey humor or sympathy, especially dry humor that could easily be misconstrued.
As one friend on Team Emoticon put it, "Communication is 90% nonverbal, so when conversations are distilled to texts, it's impossible to pick up on tone and body language, and thus easier to read your own assumptions into the text." And because unless a guy includes three smiley faces in an email to me, I'm like, OMIGOD WHY DOES HE HATE ME? WHY AM I SO ANNOYING???" Which is when our chat window closed suddenly.
You are also allowed to wink ;) to convey innuendo or mild flirtatiousness, but please, when propositioning someone, use actual words. Even booty calls deserve more than this: 8====D~~~~~* (_*_)?