I badly miss a page down/up key. I've encountered this problem in a few situations, but it's gotten a lot worse now that I have more than 5000 songs in Someplayer, adding up to about 1100 artists that all appear in the library. I can scroll like mad a few times and blow through the list in a few seconds, but it's not very precise at all (especially since it tends to stutter); alternatively, I can type in a letter and it gets me to it, which helps.
I'd like to be able to use the scrollbar, but from what I've read during a quick forum search that's a non-starter as Maemo doesn't implement it and it never got patched in by the community (unless I got my info wrong).

I can use the arrow keys to move through the list, but it's very slow, as you'd expect; I'd like to be able to page-down through the list, but I can't find a shortcut that'll work. The wiki suggests several including space (which in someplayer just selects), ctrl+down/up (doesn't work), and the volume keys, but those are just for a special Evince mode and don't work outside of that.

Can a universal page-down key be bound in any way?

You could remap the keyboard (http://wiki.maemo.org/Remapping_keyboard -- one of the first examples include a page-down kley).