Having sailed 3 Tybee 500s in an array of conditions, this is a topic that is pretty important to me. I've learned a lot. The most dangerous place to be is at the back of the pack and we almost got in some serious trouble whith a sailor entangled and the boat going turtle. A boat about 1/4 mile ahead later remarked that they saw our daggerboards in the air and "wondered about us". They didn't turn around and at that time and place and with my experience level at the time, I might not have either given our relative positions. However, I would now.
This past year, we saw a team about 1/4 mile or less behind us flip and could tell that a sailor was separated from the boat. There were still several boats behind and we kept a close eye on them to make sure that someone was assisting. Once we could clearly see that they had assistance, we stopped considering them. That same team on that same leg (a rather experienced team too), after flipping again, found themselves well back from the fleet. A third capsize left a sailor separated again but nobody close enough to see that they had problems. However, they had done something very right that day that I have not been doing - but will be in the future. Each sailor had a VHF radio on their person and the sailor in the water could communicate. I believe the Coast Guard spotted them before any call for aid went out but at least they had a slight chance to call for assistance or help themselves be pinpoitned.
Here's a couple things I consider law: For distance sailing, if a boat ahead of me is having a problem, unless there is another boat in MUCH closer proximity, I will always sail by and check to see that they are OK and under control (no matter their experience level). If a boat behind me is having a problem and there are boats behind them, I will make sure they are getting assistance from another boat. If a boat is behind me and there are not any (or very few / spread out) boats behind them, I'm turning around to offer aid.
In addition to these things, I'm going to start carrying my VHF radio on ME. I know broadcast range is very small when the radio is 12" above the water - but it would serve me a lot better than if it were on the boat floating away.