Double explosions

...otherwise known as double exposures.

After seeing a tutorial on how to do this in photoshop, I can't stop. I'm not that great using Photoshop yet but I'm trying to learn a new trick every day or so. What I love about lomography cameras is that you can do multiple exposures in one frame, that's what hooked me on the holga when I was a teenage. Of course, doing it digitally does feel a bit like cheating but there is the plus of not wasting film on potentially bad shots. 

What do you think? Are there any good photoshop tutorial sites I should check out?