The biggest issue people have been running into now is database size. We're now at the point where the amount of space for storing MP3s on a laptop hard disk has outstripped the limitations of the player's song database. You can now build a player with room to store more songs than the player can successfully index. This problem is mentioned in the drive upgrade guide, but not much detail is given. Basically, if you have more than 10,000 songs in your MP3 collection, you might want to only load a subset of those songs onto a player. There are some workarounds, discussed in a thread linked off of that drive upgrade guide.

SSDs work if you can find an adapter that works and fits inside the player.