DIS meets depend on how active your DIS meet thread has been. Our first cruise was the inaugural western and we had about 5500 posts when we cruised, with about 40 DISers posting. I think about 30 or 35 showed up at the meet. We had shirts made up, and someone brought lime green lanyards with our board names, etc. All through the week, we were meeting and talking to each other. It was awesome, feeling like you really knew people on board.
Our 2nd cruise was on the Wonder, and we only had about 3-4 families post on our meet thread. No one showed up for the meet I set up.
So if you have a very active thread, you'll probably get about 2/3 of the people at the meet. A less active thread might see 1/2 to 1/4 of them show up. It seems to be more likely on the 7 day sailing than the 3-4 day sailings.
Enjoy!