Tool/weapon durability is extremely important for Cataclysm. I hope it gets done sooner rather than later. It’s not terribly difficult to get all of the tools you need to do just about anything together in one small area, and then you never, ever, ever, ever, ever (get the idea?) have to worry about it again.
The game should encourage more scavenging, and tools and weapons are a little too easy.
I think the way I’d probably handle it is thus:
Every tool has its own chances of losing durability for certain tasks. For example, a wrench:
Primary Use(mechanics): 0.5% chance of losing durability. Secondary Use(example: hammer alternative): 1.5% chance of losing durability. Weaponized: 1.5% chance of losing durability. Each time the tool is used it runs the percentage and if you’re unlucky, the weapon degrades by 1 durability point.
Each tool has an amount of durability. For a manufactured wrench this might be 8. For a makeshift shovel this might only be 2.
The (remaining) durability of a tool is also directly related to its effectiveness. At low durability, tasks take longer and the crafted item may start with lower than maximum durability itself.
So a makeshift shovel at max durability (2) may take x2.0 longer to dig a hole. A manufactured shovel may have a max durability of 6, but if it has been reduced to 2 durability through wear and tear, it would also take x2.0 longer to dig a hole. So durability can remain a constant across all usages and all tools.
Tools with very high durability (very high quality tools) may actually confer some benefits, speeding up crafting times and maybe even making superior tools with more durability than normal.
This allows you to tie durability and item quality into one simple system. Superior items have more durability and last longer than other tools. Shoddy tools start with less durability. Certain kinds of tools may be less or more prone to damage. A stone hammer at durability 2 and a steel hammer at durability 2 (due to degrading) will be just as good at their tasks, but because the manufactured hammer is made of quality materials it will have a lower chance of degrading further than the makeshift stone hammer.
Durability can also tie directly into weapon statistics. Superior weapons have higher durability and confer higher damage, and/or higher to-hit ratings, and/or lower movement costs. As the weapon degrades these stats decrease as well.