h'mm didn't realize it's been a year. I'm still working on other stuff right now but i'm going to try to release something eventually.
I'm not too sure about coral cache's uptime, but since it's distributed over lots of servers, I would think it would be high.
File uploading is transparent. You basically change a part of your url and the cache downloads from your site to cache the file. From there is uses the cached copy to distribute the file. It's supposed to hold the cached copy for 24 hours unless the file is changed or or the coral cache is flushed. Theoretically, under ideal conditions you would only see 1 download of each file a day.