bedroom with curtains

I've been searching the forums for curtain material, and have found a few, that apparenly look to work very well. The only problem is, I havent been able to get any of them to look anywhere close to right in my renders. I used the curtain-massimo material with unimpressive results, and let it render on MLT all night. (4 cores on an i5-750 Intel)
It's grainy, noisy, and the curtains look terrible, the door glass reflection looks unreal, and the whole scene is washed out.
You can download my scene here 11 MB

missing a lot of textures, you must save file as file with textures, and zip them all into a shared package.
my guess from the render is that the lighting needs a lot of work.

As Fletch said save the scene as file with textures. I would let the exposure to 1 and enable "volume lighting" under settings-->scene-->global settings (as stated in the post with the material).

Also please bear in mind that a material is not good in itself. It depends a lot on models, lighting, settings etc. If you use a good material on bad models or with bad lighting the result will be bad. I'm not saying that your scene is bad (didn't really look at it) and that my curtain material is good (for example you're right about long render times) but, on the other hand, I think . Another by FYMoro with the material in action. Those renders were made with Twilight, but the render engine is the same of KT.

ok here is the scene with textures

https://dl.dropbox.com/u/22707235/scene.zip

What defines good / bad lighting? I mean, where do I start?

Well quickly looked at your scene. Some basic considerations:
1) You have some commercial textures in the scene so I suggest you to change them if you want to share the scene;
2) Your lighting is made by the sun+a spot light+a global and also you have an image on a plane (the plane will stop some sun's light) as background. Definitely a bit messy. Also the spot light has attenuation set to "none": better always use "inverse square". As a start, and as a general rule of thumb, I would go with the sun only or the hdri only;
3) Volume lighting is disabled;
4) I would tick "soft shadow" under the sun's settings;
4) The curtains have thickness. No need for that i believe.

I'm rather excited about the results I had using some of your suggestions. I figured out how to use Sky Portals, Illuminants on triangles (inside my chandalier) and the lighting seems better than the first post. See below.

Rendered with #7 setting

I rendered it with setting number 7 which seemed to work the best. I tried rendering it with MLT but the lights in the chandalier didn't look accurate (didn't look like they were on anymore. The only question I have is how do I make it look less grainy yet. You can see the grainy screenshot I attached as well.

Grainy Screenshot

room15-2.jpg (65.86 KiB) Viewed 8526 times

It's better. You have now several issues regarding the model:
1) The pitches of the roof and the floor have no thickness;
2) Some faces are reversed (roof, floor);
3) You have only half roof and a lot of walls are missed.
The more your model will be close to reality the better will be your render.
P.S. I would also avoid pure white and/or pure black colors.

Why do the roof / floor need thickness? How much?