If you use layercut.dll in a theme to enable alpha blending with pngs, it will load a bit slower than shortcut2, I haven't tried useing a png with shortcut2 yet so I don't know if they'll slow down a loading time.

Milk: "I prefer minimal themes where there is no need for fancy shadows, so I haven't worked with PNGs up to now."

You might really like what you can do with alpha blending, it's alot more than just shadows. For example, a simple anti-aliased edge on a graphic can turn out a lot cleaner (imho) and you just can't do that with magic pink, you either end up with jaggies, magic pink corruption, or both. :/