If you want to discuss (argue against) MY opinion on the matter, make a new thread and I'll happily devote some time to why I think the way I think and why "but they didn't do it in 3.5 or 2e or 1e!" is the most retarded argument I could ever think up. Otherwise, we're just monopolizing this thread about what DMs do on 1s and 20s with your arguments against one poster's opinion.
See, the bolded part, imho, is the reason this thread got derailed in the first place. It's the way you're expressing your opinion that rubs me the wrong way, causing me to be unable to concentrate on the real topic of this thread.
You accuse me of being overly defensive of 4e. Fine. But you are defensive about everyone who doesn't agree with you, even if your arguments have been proven wrong.
So, let's get back on topic:
I don't feel natural ones and 20s should do something beyond what they're already doing. I'm not overly fond on the Dark Sun rule for weapon breakage, either.
Natural ones are an auto-miss, and 20s do (at least) max damage. What more do you need?
Crit tables are something that is best done as house-rules, as they've always been done. Maybe we'll see something in that direction in the Unearthed Arcana series.
And then (as I've already mentioned in this thread) there will be the Fortune Cards, and the setting specific cards, like the Doom cards in the Shadowfell box to inject some random element into combats which fills a similar design space. I expect these to appeal to the same kind of players who enjoy using crit/fumble tables.