I installed Rockbox on my Sansa e260, following instructions found on this website step by step. My player would only function for about 1 minute before crashing. The LCD would either fade to white, the screen would be filled with gibberish, or the unit would just freeze.
In the two minutes I was able to listen to mp3's (that plays w/o incident with the shipped firmware), there was a 12-20 second delay when adjusting volume or switching tracks, followed by another total lockup.
Loading themes also caused the player to freeze up.
So, that's been my experience with Rockbox. I just want something that works when I turn it on, not something I have to fight with.