I thought I would try Rockbox on a new Clip Zip. Installation is straightforward. Removal using the Rockbox utility is incomplete, it doesn’t tell you that the final power up requires the original firmware boot (left button while powering up). I figured this out, it sort of has to be that way since the modified firmware will still be in control until replaced, but the manual should have mentioned this.
For installation, use the Rockbox utility. For removal, just copy the original firmware to the root of the clip then boot to the original firmware. I would remove the card to avoid spurious media refresh (you will get one when you replace the card). Since I didn’t have anything on the unit, I did a format. Otherwise you might want to manually remove Rockbox stuff.
As far as Rockbox itself, I can see why others might like it, but for me the menu text is too small. I bought the clip zip for improved fm, apart from that I dont see much difference between between the models. FM on the clip zip is easier than with Rockbox. Music menus are marginally better with Rockbox. The biggest plus with Rockbox is better refresh, but I rarely do much in this area.