Depends on what you want to do. Most of the images are in SystemUI.apk, framework-res.apk, and RES_cappuccino.apk. If you want to swap icons, change images, etc, most of that just requires swapping out PNG's, which I made a tutorial for here:
Swapping out PNG's
Other edits, like sizes of text, carrier locations, etc might require XML edits:
Editing XML
But it's pretty extensive what you can change. Here are a couple of shots of a few things I changed and where I edited since I, like you, was so repulsed by LG's sense of style =) Almost everything I did can be done with just XML edits and PNG swaps.

Changed notification bar icons (SystemUI.apk PNGs, and a handful in framework-res.apk)
Percent battery (framework-res.apk edit)
Invisible pattern lock (framework-res.apk PNG swap)
Transparent notification bar (required deodexing as well as PNG swaps in SystemUI.apk)
Remove carrier from lockscreen and notification bar, and removed clock from bar (XML edits in framework-res.apk and SystemUI.apk)
Detached lockscreen clock font from system fonts (requires deodexing and then swapping a font file)

Transparent pulldown background, notification bars, indicator bars, etc (PNG swaps in RES_cappuccino.apk and SystemUI.apk)
It's actually been a lot of fun learning how to do all this =)