To me the way the quick launch area in the taskbar is managed is ideal: you can adjust it's size, remove items from it, and items that don't fit within its area fold out when you click on ">>".
My idea is simple (am not saying it's simple to implement, no idea!): make the system tray work exactly the same way
If that could work it would be nice to define "rules", so the utility knows ahead what to do with a new icon (for example keep the USB icon in the tray, to be able to still manage removable media quickly).
I know many utilities exist, but none has satisfied me, and with the popularity of netbooks (with small screens), I think this would be something popular.