I have downloaded it 3x, and attemped to install it 3x. Each attempt ends with failure and advice to contact the software manufacturer.
What's your source on that?
I'm pretty sure I've used and installed the Kindle plugin on a Mac, not sure if it was CS5 or CS5.5.
It was just for a quick test, not for real work, so I don't have any experience to share. But it installed...
Amazon's Kindle plug-in definitely works on Mac OS X 10.6.8. You have to follow the instructions that Amazon provide for downloading their code-signing certificate and installing it first, or the plug-in installation will fail.
If you have InD CS5.5, it probably isn't worth it, though, The Amazon plug-in only offers the options that were available for epub export in CS5. I had more success exporting epub from InDesign, so I got to use the more powerful new options, and then opening the epub in Kindle Previewer, which you can also download from Amazon. It's mostly for getting an idea how the book will look on Kindle devices, but in the process it translates the epub to .mobi, which you can then send to Amazon when you're ready to publish your Kindle book.
I did have to crack open the epub and edit the CSS and one of the XML files to get anything remotely acceptable.
If your layout is anything but a simple text flow with some anchored images, you will probably find the Kindle version disappointing. I'm waiting for the new Kindle8 tools to be available before trying anything ambitious.
yes, the kindle previewer shows you what it will look like in an original kindle (horrid), kindle dx and the kindle apps for iphone and ipad. it also gives you the option of opening the book in the mac kindle viewer if you've installed that.