Noise isn't determined exclusively by ISO. In fact ISO has only an indirect effect on noise. Noise is principally the result of there not being enough light. Therefore it may be the case that your ISO 2000 are genuinely too noisy to be of value. But someone else's ISO 2000 might look a lot better.
Personally I've used ISO 6000 and 8000 in the past, when working in very low light where flash, wider apertures or longer exposures were not available (I was shooting 1/50s at f/1.2 with an 85mm lens).
In fact I would never put a limit on the ISO used, I would capture as much light as possible and then set the ISO as high as possible without clipping highlights. This guarantees you the lowest noise level possible. If the images didn't look acceptable to me I wouldn't use them. But I would never say "ooh I shouldn't set the camera to ISO 10000 as there'll be to much noise", you never know until you try.
The following were all shot at ISO 6400: