When I work with 8-bit images in Photoshop I never achieve to get smooth gradients when working with dark colors. I looks bad and it's a clear line between dark gray and black. My guess is that is because I work 8-bit files but is there any reason at all to not use 32-bit images on the web? Sure, they have a greater file size but is that the only reason? It doesn't have anything to do with web browsers and incompatibility with 32-bit images?

Why not design your images locally in 32-bit mode, then convert them to some other format for publishing.

There are a number of different image formats, which allow you to trade quality for size. Pick the one which fits your needs.

That's true, I can always convert them later on. But is there any reason why the standard is 8-bit (or is it even a standard? do I just have a distorted world view?)

If you're using GIF as your file format, then yes you're stuck with 8-bits and that can get pretty crude at times.

By and large, you should be using
PNG - for computer generated images.
JPG - for photographic images.

IE was the last of the browsers to support PNG properly, but that's been fixed for the past 4 or 5 years.

There are several sites (search:IE PNG fix) which allow you to fix PNG in older versions of IE. But check your server logs to see how many browsers connect with IE versions earlier than IE7

But when in Photoshop about every option you can choose with layers are grayed out when working with 32 bit and a great number of filters are grayed out when working with 8bit. So am I limited to 8bit if I want to use any creative built in functions in Photoshop?

Yes you limited to 8 bit, bcoz it refers to the color management,filters, effects and gradients will not allow you to apply because of referring to lower bits.Image mode will give you the options enabled in higher bits.

Is there any way around this? Like working with 2 psd documents, one 8-bit and one 32-bit, and copy pasting into the other?

Not Posible, while you try it will ask for the mode change or automatically converted to lower bits I think.

Then how do people work with dark colors and still get good result?

For that not only the solution is 8 bit or 32 bit. They will also use image works like curves, brightness darkness, illuminations etc. That will give them the output as you say.

Ok, thanks for the good answers, it has helped me a lot! I guess I have no more questions :) thanks again Rajarajan!