Almost no one uses it anymore. I recently renewed my sub and was surprised how long it takes to get a dungeon group with LFG. I may get another DPS or a Tank after a while, but whole group ... that's another story.
You either have to spam general chat or stand in front of dungeon entrance and whisper to people around you.
It has never been a good tool, as it was designed and implemented in an hour or two, but I was hoping something changed for the better while I was away.
It has gotten worse. After launch I was able to do all three level appropriate dungeons without much fuss and waiting. Using LFG. Now, I am lucky if I manage to do one of them before my level become too high.
It makes me feel I am playing with just a fraction of players that were there at launch.