For a laugh I decided to go outside around midnight and take pics with no lighting, pitch black dark outside, used the 25000iso (yeap25k) and was kinda shocked that it gave me a detailed image, although grainy and somewhat yellowish...amazing
My 30d only does about ISO 3000 but last summer I took pictures of my family sitting around a camp fire, without a flash and using only the fire as my light source. I came out with some get shots that look really interesting. Some of them could have been better but I didn't have my tripod with me, but I found it was them moving that was causing me more trouble than camera shake.