But things started to get really interesting once everyone was capable of reliably accumulating more gold than practically necessary (I preferred hunting liches on the fourth level of Deceit) the de facto currency became overt displays of wealth. The built in prices became meaningless. There was a market for housing that differed in interesting ways from shard to shard. There were whole malls that housed secondary markets for bulk purchases of reagents and crafting supplies.
I literally went furniture shopping for my house at the carpenter shop in the mall run by Dragon's Claw in a castle outside Britain... and while I was there, I probably picked up some regs.
As a player, I remember the early days of the pure black dye tub. IIRC I bought my first one for 25,000 gold [edit: for reference, a boat cost 15k, and a house deed, 40k] and instantly dyed everything I owned this anti-color. It was a very trying time, waking up not knowing if your valuables were still there. But it's really interesting to read the events from the perspective of a very reasonably upset artist. The way they ended up handling the black dye tub, however, became the sort of precedent for this type of incident.
The most compelling aspect of UO was the diverse ways in which people made use of the world and its resources - and OSI seemed to be, on the whole, fairly receptive to these things. One other good example was the practice of "Server Wars." Every Sunday morning, the server would save and go down for updates. When this happened, everyone would get a grey message after which no activity would be saved, but the server would stay up for a while. This became the worldwide cue to go to your local graveyard for a colossal melee which would be wiped away when the server came up.
I could go on at great length about other ways in which the world of UO was great, but I'm moving tomorrow and really need to sleep.