The answer for me is: it varies. I like to know everything my character would know about the world, and nothing about what he didn't know and that I wouldn't need to know to realistically portray my character in the setting. For example, I'd like a lot of details about my character's city or region, about the customs and superstitions of said city, a little about its history, the descriptions of its places, etc. When the world isn't really that developed to have these informations, then I'd feel free to create some of those things as I go along. At the same time, I like the feeling of discovery, of surprise and of the unexpected. I try not to bother with things my character doesn't know, because when they discover it, then I'll be surprised as well.
So I guess it varies on how much creative freedom you want to give your players - are they allowed to create customs and places of their city, maybe even an entire city? They need less details. Are they supposed to portray their characters realistic in an already developed world? They need more detail.
When someone is describing a room/place our characters are in, I automatically allow myself to fill in any details not described (unless the game has a DM/Storyteller/GM, of course, then I'll only ask what my character can see or sense). So the amount of details also depends on how you want the scene to go.
Summing it up: I love details, as they give flavor to the world and how I create/play my character. However, too much detail (every single plant described, even if they are the same as our own plants, every color of every furniture in a room, etc) can get bothersome and tiresome. Too little (saying the character are in a room, but not describing at least what kind of furniture is in there), and, unless you give people the freedom to create details as they go along, the ability to realistically RP becomes hindered.
I think you should first think what kind of details are important for your players to know so they can realistically interact with the environment they are in and describe those things only. If something is missing, someone will surely ask. Never, however, reveal something the characters cannot see/hear/smell/know.
Just my thoughts on the matter. :)