I know the question is a bit subjective, what I'm after is if there is enough improvement in jpeg2000 and enough support in software (image viewers, browsers) to warrant using it.
I will respond by referencing the reasons for defining the JPEG2000 specification in the first place, which, when you read it, will explain why you don't see or hear about it:
So, JPEG2000 was created to improve image download time, and the fact that digital images were getting larger. Now, while we still need to care about optimizing JPEG for web viewing, and something like JPEG2000 would be nice, times have changed. I think this is dated thinking, as the expansion of broadband, dynamic image loading of JPEG and auto-sizing found in sites like Flickr and Smugmug to name two, have really eliminated these issues. Rarely do you run into an issue where a DSLR JPEG is 'too big' to show on a screen. Not to mention that screens are higher resolution and much larger than they were in 1999, when the specification was proposed.
This was made a standard in 2000, and is supported by most browsers, but I suspect it isn't used because it doesn't solve any problems.
I think no one cares. Note that JPEG XR/HD Photo have been created since, and no one seems to care about them either, not even Microsoft, who hasn't updated their HD Photo spec or info since 2006.
The real question is, what is the usage of jpeg2000. Since most websites only support JPEG, BMP and other 'standard' formats, mostly you won't use it for websites. For storing pictures, I personally use .NEF (Nikon RAW format) and I will always recommend RAW for every (non-casual)photographer.
I would appreciate it if someone would add some usage for JPEG2000 to this question, so that it will be answered more completely.