The largest category of application skins is probably OS X-emulation. It is possible to get a realistic screenshot of OS X on Windows. However, after using OS X, then using Aquafied Windows, you should be able to tell the difference.
Some apps add something on to Windows, like FindeXer, that I find useful even when not mimicking OS X. Others are annoying, like the Finderbar instead of the taskbar. Using Alt+Tab to switch windows is annoying for me.
Some good links for Aquafication, or OSX Emulation:
Aqua-Soft | A very active forum community that can help with almost anything, but especially OS X Emulation
OSX-E | The best site for Aquafication, it has everything you need to download!
Flyakite | The lazy person’s Aquafication software. Download it and it installs everything, including system file mods!
The Manual | There are many manuals on Aquafication, but this is the best.
