Well, I would do it myself, if I even had the slightest knowledge as to how to. The PRX customizing guides I've found have been kinda confusing for me, otherwise, I would really attempt it.
But, I thought of a good idea, in MY opinion..
An iPod Touch or iPhone theme that utilizies the PSP's rotating functionility (sp.?)
As in, turn it 90 degrees to navigate through the XMB.
I don't know, it just sounds cool.. :/ Just a suggestion, incase anyone wants to give it a try, since it sounds really nice to me.