I miss the keyboard on the HTC Dream/T-Mobile G1[0], it hid behind the screen until you needed it, so there was no need to sacrifice screen or keyboard size.
Being able to feel a text or other message come in, pulling it out and popping the keyboard to activate the screen, reading the message, and then being able to type my response with two thumbs without looking at the screen was a delight.
Plus the one window per conversation thing across all protocols (it was IIRC libpurple backed) worked -really- well due to the extremely good window switching system.
Oh, and a resistive touch screen which meant (a) tactile feedback (b) it actually worked in mild rain.
Ok, it was significantly pants at pretty much everything else, but as an upgraded pure communications device I don't think I've ever liked anything better (remove 'upgraded' and it and my beloved series of 6310i dumbphones are neck and neck).
This one hides away, so the "takes valuable screen real estate away" angle is not valid.
So instead, beware of dust!
Anyhow, have no idea why they would be dust traps. People's cases are far worse for that.
(I don't use a case)
I'd love a "modern" phone that's a slab with a landscape slider keyboard. Don't care if it makes the phone thicker (especially if they use the space to cram in some more battery capacity).