Low light performance is one of the most important factors I consider when buying a camera. At one point I did an expensive switch from the Canon system to Nikon, when the D3 came out, for its amazing high-ISO performance (I returned to Canon when the 5DmkII came out).
On a popular forum for users of Micro Four Thirds cameras (which struggle beyond ISO 800), a poster recently questioned the rationale for high ISO performance, stating 99% of users will never shoot beyond ISO 800. I quickly looked at my statistics in Lightroom, and found over 54% of the photos I took in 2011 (to date) are at higher than ISO 800.
That begs the question: who is more representative, him or me? Flickr.com publishes statistics on popular camera models, but apparently not on other interesting EXIF metadata. I whipped up a quick and dirty Python script to sample recently uploaded photos from Flickr and collect the ISO speed from their EXIF tags, when available.
Of 3020 photos I sampled, fully 399 were shot at ISO higher than 800, or 13% (the 95% confidence interval is 12% to 14.4%). Thus significantly less than my proportion, but far higher than 1%.