The API call simply returns the data in gzipped and Base64-encoded format.That's what I suspected, but I can't seem to get uudecode to give me anything that looks like gzip in its output. The sizes line up, but there's no gzip header.
Berend also noted that the bits about the chipset being Altheros and MIPS are well documented in press releases. Cool! I'm not just making this stuff up! Let's quote from there:
The solutions also come with full driver support for Windows Mobile CE 6.0 and Linux-based designs.WinCE does not have a 'devfs' as far as I know, so that would lead me to believe that the card is either running Linux or EyeFi has ported another OS to it. That would be a wee bit interesting if it ran Linux.
Although, the card can't be running Linux since it is GPL'd and would require EyeFi to publish the source code for at least the kernel. They aren't doing that as far as I know, so it can't be running Linux. Just in case, here's a nice informative link which clearly explains a company's obligations under the GPL.
(changed "a commenter" to refer to Berend)