I did it once with visitors who really really wanted to go. It was for the year 2000, and I figured if ever there was a time to do the New Years in Times Square thing, it was then. Remember it was a high security year - even before Sept. 11 everyone was sure there would be some sort of terrorist attack. But we saw Rudi and Hillary mingling with the crowd and figured it was safe enough. Undercover cops mingled through the crowd too but pretty much ignored the low-key partying going on everywhere. Bigger fish to fry?
Once was enough for me, but it was definitely unforgettable and I wouldn't ever deter anyone from doing it. The people with me were absolutely blown away, not only by the sensory spectacle of it all, but by the smooth operation and the professionalism and friendliness of the cops. I was not expecting that either, to be honest, but they really do a good job. The barricades keep you from being crushed, and it wasn't claustrophobic at all. I was very proud of our city that night. Over a million people from all over the world not only reasonably well behaved but having fun. Your surroundings keep you amply stimulated and anything but bored. Even though no toilets were made available, people who really had to go somehow found a way out and back in through the barricades, so there were very few negatives. However, the advice I would give to people is to try NOT to have to go to the bathroom (don't drink, wait until afterwards, or at least until midnight). You may or may not find it worth it all in the end - I did, to my own astonishment.
One of the most impressive things for me was how incredibly fast it cleared out after the midnight celebration. Fast, easy, no wait whatsoever. Completely opposite of the National Mall for the Inauguration, where you could barely move trying to get out.
And now, every year when I'm watching the ball drop on t.v. I can totally relate to everyone in that crowd. They really are having a great time.