I've had these blocks of Sennelier Watercolor paper that a friend gave me for quite some time. The problem was that the pages were glued together so strongly that I had the worst time trying to seperate them, and always ended up tearing the paper.
Recently, I bought an Unblocker from Cheap Joe's. It's just a little plastic tool but oh, my it does the job! Now I can use these blocks without fear of ruining what I've just painted. Note, that a plastic knife might (might) work almost as well.
This was a quick study I did without any photo reference after we did sunsets in my watercolor class. It brought home to me how much the paper does matter. The paper can effect the colors and textures of your paint.
I found the colors (Gamboge, Cadmium Orange, Naphthol Red (just a touch) and Ultramarine Blue) were more muted and subtle than with the other papers I had used. The texture of the paper showed up more. I like it!