I currently have Rockbox running on my Sansa e250 player. It is marked "Rhapsody", but after some investigating, it was determined that it isn't really a true Rhapsody player & therefore I was able to install Rockbox.
I love this Rockbox interface over the crappy Sansa and it feels like I have an all new mp3 player. Anyway, I have heard that Rockbox on some Rhapsody players has some limited functions. I can't imagine it getting much better than what I have, but I also wonder if I have the "limted" version since my player is marked "Rhapsody" on the back. If so, I was just curious what the limitations are.