One of the book's readers recently was disappointed to discover that Lightroom doesn't support PNG files. As his note explained, "When I pointed [Lightroom] at a folder to import pictures, it only “sees” JPG images. The PNG are ignored."
It's true: Lightroom, which is aimed squarely at digital photographers, does not support PNG. (Here's a list of what formats Lightroom does support.) The main reason: digital cameras don't use PNG. But that's only part of the answer. The larger answer is that Lightroom is no substitute for Adobe Bridge, which the company bills as a media manager for "all your creative assets." While you can't buy Bridge as a stand-alone product, Adobe includes it in all its Creative Suite combos, as well as with Photoshop, Illustrator, InDesign and Flash. Notice Lightroom's absence from that list.
While I use Lightroom everyday for tracking my photos, I depend on Bridge for keeping track of all kinds of other images. That includes PNGs and anything else I don't' want clogging up my Lightroom catalogs. For example, in writing these books I take literally thousands of screenshots using Snapz Pro X. By default, they all go into a special folder named, well, "Screenshots."
Within Bridge, I've marked that folder as a Favorite which allows me to jump straight to its contents. If I was using Lightroom to keep track of those screenshots, I'd first have to import them, then apply a keyword or two to make them easier to find. That's too much hassle for images that really have nothing to do with my photo work.
Make no mistake: Lightroom's a great tool and serves as my main hammer. But not every image is a nail.