I'll let this image do the talking for me, at least for the most part.
It's kind of amazing that we can now get
usable photos at ISO 25600 these days, eh? If you've thought that's insane, I think the latest Canon and Nikon full-frame DSLRs can shoot at ISO 102400 without breaking a sweat. Then again, the NEX-5R is "merely" APS-C. It feels very strange to be able to use such a high ISO when you come from a cameraphone background. My smartphone can barely handle ISO 800.
(By the way, full-frame (35mm-equivalent) DSLRs from about a decade ago seem to have about ISO 800-ish equivalent. Technology advances, anyone?)
I think ISO is actually something that makes a lot of sense to improve upon, eh?
(By the way, the iPhone 5's reported ISO seem to be able to go as high as the lower 5000s...)