A small issue with Mercado

Andrea Mercado writes in her blog post "Tagging on Flickr & del.icio.us" that one of the ways in which to find other users bookmarks on del.icio.us is via "Browsing, [kinda like the bookstore browse vs. trying to find something on a library shelf using the call number system, serendipity vs. structure]." I take issue with her suggestion here that serendipity and structure are opposites. Yes, library materials are arranged according to a highly codified system, but I see no way in which this somehow hinders serendipity. While a user may use different information seeking methods when they start searching in a library vs. a bookstore, I would suggest that many end up browsing just the same in the end. Collocation allows for highly successful browsing within the library and serendipity is just as likely to strike in the stacks as it is in the aisles of a bookstore.