On PSP, the icons are well readable on default themes, but often if you put a photogarph as a wallpaper, the icons are easily lost and hard to read if there is a lot of detail in the photo.
I'd guess the user profiles might allow for some sort of customizability, like arranging the icons in a different order and removing unneeded icons (like remove settings for the kids and wife etc...)
I don't think they're too small (note I've only seen the pics), and being simple in design makes should make them easy to recognise. It might however be good if they accenuate more the icon that's been selected. In PSP it's just a slight glow and size increase to the selected icon, but because of the "cross design" it really doesn't need much else as it's virtually impossible to get lost.