Vector Skin

Note: You can do this by adding the following to your /vector.js:

/* Make all of the links lowercase */
div#p-personal li { text-transform: lowercase; }
/* Override the lowercasing for the username */
li#pt-userpage { text-transform: none !important; }

To be honest, I also prefer it to be lower-case in this situation, though I'm otherwise someone who cares for proper capitalization.