Hi Damien,
I finally made time to read the Levels class today (I didn't want it to stop though, I felt so sad when I got to the end, I wanted to keep learning!) There were two things in particular in that class that made me jump with joy when I learned about them (I'm probably not allowed to say which ones ;-)
I have just edited my first "hand-edit-only" photo without the use of any commercial actions. That's a major breakthrough for me. Ever since I bought my first action I've always been wondering "how do the actions work, what exactly each layer does, how do I make it from scratch" and thanks to your Levels class I've made some great discoveries. Now I can edit on my own (well there's still a lot of things I need to learn obviously this is just a start, but oh the excitement!!!)
Thank you and I hope you'll be making more classes on PS ;-)