The NASA World Wind servers should now be back to normal, the problem was not hardware failure luckily, but aggressive server scraping, the country the scraping originated from often gives World Wind Central trouble too.
The NASA team are happy to share data and tolerate lightweight scraping, but it seems that some people just aren’t happy with that, it is slightly amusing though as all the data on the NASA servers is available elsewhere and free. If anyone does need a complete set of the data I would suggest you contact NASA directly and just ask, you may only get the raw data though as a lot of World Wind’s imagery is created on-the-fly.