I've heard so many women bitch about men who use a little :) or ;) in their text messages. But I actually like it, when used right. I think a little well-placed emoticon usage can go a long way, and here's why:
Tone is so hard to convey via text or email.
We've all bemoaned the non-existance of a universal sarcasm font or sign at some point, right? Well, barring any other options, the winky face is it. Want to make a smartass joke and be absolutely certain that she'll know you're joking and have fun with it? Insert ;).
It's much better to wink than be sorry and spend 10 texts back and forth trying to explain your joke.
It shows you can be playful.
Yes, there is such a thing as overdoing it. I don't want to see a smiley face in every damn text you send. But every once in awhile, it's good to know that you're sitting over there with a smile on your face while you're texting me. I worry if everything is gruff and dry and boring.
It's easy to flirt and be a little suggestive by just adding a wink or a smile. No need to spell it out and get too explicit. Drop a little innuendo, add a wink, and you're set.
But don't overdo it.
There's a difference between playful and flirty and too much. You don't need a wink in every text. They lose their effect and make you look soft.
Also, never ok: [smile] or anything like that. Just no.