Silverblade - I liked the old weapon materials rule. And in old Dark Sun, you could have magical (or psionic) bone weapons. However, penalties to attack and damage are a big pain in the butt, but I want to encourage that metal items are better. A simple breakage rule works for me - if PCs break their normal weapon, well, they carry spares (hey, I remember in 2e, every character had multiple weapons... had to have a club for those skeletons!). That, to me, is a lot of fun. Plus, it's only a minor action.
Losing your magical weapon sucks, but it only applies for the rest of the combat. And then it's fine (you resharpen it, or whatever).
Anyways, I think it's a simple technique, and it's the one I have in mind - if the 4e design comes up with something better, I'll be taking it.
And KM - I have high hopes for this one, too. But I also know that sometimes, that can hurt me. So, I'm going into this with a "I'll have to do a lot of conversion, but the 4e book will help out with some ideas". Which I think will stop me from being hyper critical of it ("What!? They don't mention that thri-kreen prefer to eat elves! They've *DESTROYED* Dark Sun!").
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In the past, my Dark Sun games have been very sandboxy. Usually, I'd give the PCs an adventure site they could explore ("The Castle by the Yellow Lake"), and only have it very loosely sketched out in my head. The PCs would have to get there, and I'd use meticulous Encounter tables to build up many mini adventures on the way (and often, these mini adventures would be pretty built up - I love "winging it"). The whole time, they'd discuss what they thought was waiting for them in the Castle By the Yellow Lake... and I'd pick and choose the ideas I liked the most, and run with that.
My personal favourite thing about Dark Sun is how it is a game that is always in motion. It deals with the three major adventure types - urban, dungeon, and wilderness. PCs can play around in an urban area. But when things got tough, they'd go out into the wilderness for awhile, do some exploration, and find a dungeon. Get some money... and find their way to a city. And repeat.
Lots of fun.
Also, my other favourite thing on Dark Sun (and something I *have* to preserve, 4e be damned!) is how easy it is to screw over the players (and how much they love it!). In 2e, you would functionally start the PCs off with leather armour and the equivalent of cursed weapons. After a couple of adventures, they'd work their way up to sort of okay armour. And they'd go crazy for metal weapons... items that are, compared to their normal world counterparts, starting equipment! Not to mention that if you did piecemeal armour, you could reward PCs with decent armour one piece at a time! Really, it slowed the power curve of the game down - plus, if you ignored some rules (Create Water!), even high level PCs would be afraid of the wilderness. Dark Sun was a game where I could keep the players poor, and they loved me for it.