When I was younger, the only abbreviation I remember using was PHAT. But that was before cell phones, and texting. Now, there is a whole new language out there full of LOLs, OMGs, IDKs, and a plethora of others. And they aren't just restricted to text messages, emails, Facebook and instant messaging. People use them in everyday speech too.
As writers, we can't know which speech pattern trends are fleeting and which are here to stay. And since a manuscript can take years to write, edit, and publish, anything we write using trendy dialogue might be completely obsolete by the time the story goes to print. I sure can't imagine taking a contemporary YA novel seriously where guys were referred to as "scrubs" and people asked each other if they were ready to "dip" when they wanted to leave. Will teenagers in ten years feel the same way about OMG?
Personally, I avoid slang altogether. Just like I avoid referencing specific band names or song titles which could just as easily date my story. But, does that make the dialogue less realistic? Or does it matter, as long as it's neutral? I figure, dated dialogue would be much worse than dialogue which doesn't seem to be related to a particular era (unless I'm going for a particular era of course ;) ).
What do you think? Do you use slang in your writing? Do you have a way of deciding how much slang/which words make the cut and which don't?