Brick and mortar bookstores are much better for (un-directed) browsing than online stores. This is probably mostly a function of bandwidth, i.e. I can see so much more in a bookstore than I can on my 2D screen. This will change as the web and its attendant hardware/software develops over time, but my guess is that a satisfying browsing experience of the order i can get in a great bookstore is many, many years away from practical. On the other hand if you know what you're looking for, online shopping excels at simplifying the process of making the transaction. In fact, in every sense except immediate transfer to the buyer of the object they've purchased, online buying is vastly more efficient. When the bulk of our book purchases are in electronic form, and therefore delivered instantly, the significant advantages left to the bookstore will be the superior browsing experience, the help desk and the cafe.
Ah, the cafe. I have loved browsing in cafe-less bookstores, particularly the formal old-style ones, with books separated by publisher. Tho I've only rarely browsed books because I liked a publisher's other books, it could certainly be engineered to happen more -- see If:book. Penguin, of course, brands their paperbacks using their signature design and people expect a level of quality from them. Gallimard in France also. If branding were design-based, it would give bookstores a reason to shelve books together -- visually arresting displays. Barnes & Noble does this with its classics section and did it for awhile with its miniature classics, and I have spent some time at those displays for the sheer fun of handling the books, and then bought a few because once they are in my hand they are half sold. Making an equivalent, clean, well-lighted space in cyberspace is an interesting challenge.