Its more of a 'Why I love Rockbox', but I posted this:
My Rockbox Story
A while back.
One point Saab_Rider & Spikey mentioned and I would concur with, is the standard USB port. This combined with UMS, and its just about the perfect stand alone unit (I used it to transport a 17Mb Powerpoint slideshow to college, and gave the presentation off the teachers laptop with no hassles!!)
So, with over 8 days straight worth of music (at better than competitive sound quality), a few college essays, some short vids and pics. Combined with recordable radio and then Rockbox games.......
I LOVE IT.