Check out this gotcha from their email:
The Riya uploader is PC only right now. Darn it, we know. If you are on a Mac and you can find a friend with a PC, you can upload there, then train, tag and search your photos on your Mac. We promise that we are working on that Mac uploader. Please keep sending those stats. ;)
By "PC" they mean Windows-only, so Linux (and Mac) users are out of luck.
Come on riya, don't you know all the cool kids (pronounced early adopters) use GNU/Linux and Mac these days?
