I used the PRS Customizer a month or two after I got my 505. I added the universal font size, customized icon set and of course the clock. All I can say is it was a painless procedure and I love the changes. I really don't understand why Sony's default was to use variable font sizes in their menu--just makes it look messy in my opinion.
And I'm pretty sure you can fairly easily revert to the original firmware fairly easily, although I've never tried.
dordale