For those interested, in Chris' campaign these rules come up a lot. Since there are 7 players, he likes to throw big, bad stuff at us. So far we've had two deaths, and thus far no "pop up on a natural 20" rolls. While we may get a couple of nat 20's over the course of the session, we've get to have one during play. That's anecdotal, but I think it's something to think about. If I get only a few nat 20's per session (if that many), it doesn't make me feel like I've wasted a 20 when that comes up.
So far, I like the new death/dying rules, as they're kind of building off of the 3.5 rules but with a more flexible death window to account for increasing monster damage. Besides, every now and then it's good to have a "You though I was dead, but don't forget about me!" moment for your characters, a la Merry-stabbing-the-Witch-King..