If you are worried about the software with the Rio, I find the software to be basic but useful and it works quite well for me. The advantage you'd have, is with the dock there is an ethernet port, and the Karma acts as a webserver containing a Java version of the software. This way you could just bring the dock with you to a friend's house, hook it up over ethernet, and the software files would be accessible from the Karma. Further, since it is a Java app, it will work on any OS that supports Java (re: Linux, Unix, Solaris, MacOS, etc etc).
Also, at some point down the road, the Karma should be getting a firmware upgrade for true USB MSC compatibility a la the Carbon. However, it is something that has never been 'officially' announced, so people's best guess would be when the Chroma comes out, which is looking like March. However, no one really knows with Rio.