When I got my Portable Media Centre I was a bit worried that it only (only!) has a 20GB hard disk. My previous device was twice that size and I was concerned that I would not be able to fit all my music on it.
How wrong I was. With the smaller machine I'm just putting on the stuff I *really* like, as opposed to what will fit. This means that truly random play is a series of sequential delights, rather than a voyage into the unknown. I've actually started only putting on the album tracks that I like. Being able to add Media Player ratings to the tracks on the player itself also helps a lot. So, in music, as in many things I reckon, a bit of editing is a good thing...
Oh, and one other trick. As a lover of a certain kind of beer I've downloaded all the tracks here:
http://budlight.whipnet.com/budlight.htm and put then into an "album". Added to the random play mix this works really well....