This book has a lot of surface appeal. Sullins's writing style is friendly and encouraging, Toball's Photoshop instructions in the eight tutorials are clear, and their art is gorgeous. If you are an experienced collagist/mixed media artist or scrapbooker, already possessed of a wide stock of component materials, who is fairly (but not completely) new to Photoshop and wants to expand your artistic range into the digital realm, you are likely to find Digital Art Wonderland an excellent choice. If you do not fit that picture, however, you may come to feel, as I did, that the book's weaknesses ultimately outweigh its charm.
The greatest of these weaknesses, to my mind, is that what makes Sullins and Toball's art gorgeous--in addition to their delightful imagination and sense of play--is not primarily their Photoshop techniques, but rather the wonderful assortment of materials they work with... and they give almost no information on how to find such. They refer to "photography sites and other online resources" but don't list any, except a few for fonts; they just assume that you have an extensive "digital library" and "old books" and "ephemera" scattered about. If you don't, I recommend that for starters you look at the many books of line art, most of it copyright-free, that Dover Publications has put out.
The Photoshop instructions are aimed, I would say, at the advanced beginner or early intermediate user: someone who knows the basics of the program (how to use layers and make selections and so on) but has not explored it in depth. The techniques Toball describes in the tutorials are good (I share his admiration for blending modes, and I thank him for reminding me about blending options, which I have never really explored but certainly now will), but they are of limited range; he uses essentially the same handful of techniques in all eight tutorials. More experienced Photoshop users will probably want more variety and find this pretty lightweight as a how-to book. I had a few specific quibbles as well: Toball brings up vector graphics, but he doesn't explain what they are or how to use them--and they can be quite challenging (in fairness, however, they don't play a major role in his overall technique); and I would recommend masking rather than erasing (which he uses extensively) for situations where one is likely to change one's mind, such as blocking out parts of a layer to let the parts underneath show through, because masking can be easily reversed at any time and erasing cannot.
Sullins rounds, or at least fills, out the book with a few pages of comments on composition, use of type, blogging, and the desirability of being willing to play and enjoy "happy accidents." These certainly do no harm, but for the most part they're too general to be very helpful either.