Apple's UI on Windows is an absolute train wreck. Below is a screenshot of QuickTime, Safari and iTunes running on Windows XP, I'll only install these applications in a virtual machine, I won't let them near my Windows Vista box, I don't want more background apps running all the time that don't need to be thank you. None of the applications in this screenshot are focused.
Anyway the first thing that strikes you is that ugly grey colour, I don't know what Apple's obsession with it is exactly, but it doesn't look good. Especially on Windows XP (where bright Fisher Price colours rule by default), and it looks terribly bad on Windows Vista, which actually look good.
Obviously they don't bother following the UI guidelines for Windows (not that Microsoft do anymore either), and they'd rather impose their own window frame upon you.
So what have we got wrong here?
1) Different shades of grey.
2) Different fonts, Safari is all blurry.
3) Different shading of fonts, Safari looks in focus when it's not.
4) Different sliders, Safari is the bright gel, yet iTunes is gray when not focused and just a plain blue when focused.
5) Different size and colour arrows on the sliders.
6) Window controls (close, maximise, etc) are different colours, and different sizes.
7) The resize icons in the bottom-right are different colours and sizes.
8) Search icons are different shades.
9) File menu is in line with the title in iTunes, yet a line lower in QuickTime and Safari.
10) Apple is used in the QuickTime title, yet not in the other applications.
11) The buttons between applications are completely different styles.
From a control stand point they even behave differently, QuickTime for example won't maximize, it just gets a bit bigger. iTunes can be resized by dragging the window frame, yet Safari you need to go down to the resize area and drag the window around.
So what else is there that I've missed?