You walk into a box store, say Wal-Mart to compare the latest offering of digital cameras (two people recently where I work bought digital cameras) and then in the process of talking with others who are buying digital cameras find out their thoughts on say camera A over camera B. This does not happen often in the current online world of catalogs, pictures, and written reviews.
Whereas a handful of people, potentially numerous others looking at digital cameras online simultaneously in a 'second life' online library environment, are able to share insights in real time say for example (Ralph tells Sarah a 5 mega pixels is usually enough quality for an 8.5 by 11 inch photograph done well). Sometimes, there is comfort in knowing others who are looking for similar feature sets just to say hi, share in their decision making process, and find comfort in others making the same decision: buying a digital camera.
How is this model a potential application to public libraries besides shopping? One potential is the creation of a storefront of rooms, say if your interested in science you can hang out your avatar in the science room. The library component comes in where content in databases from magazine articles, books, audiobooks, music, and visual materials on topics of interest is available for use on the storefront. Then people can leave stickies, messages, and other notes on content that is sent passively and actively to users (hey, come and view the abstract of a paper on topic x or y).
We already have library content in traditional online public access catalogs and databases in online form. The difficulty in making library content visually appealing, digital rights management practical, and practically useful to a community of users.
As for community creation and utility, one thought is that users will find other users who are interested in specific areas, just like those shopping in the Apple model and can in one sense, draw upon serendipity or off topic discussions to generate new ideas and be feed a stream of the latest research in a subject.
In all practicalness such a 'second life' library product that will be the 'standard' say '900 pound gorilla' in the room so to speak will probably be developed by specialized libraries. In general, special libraries tend to be narrower in collecting subject areas, with greater depth in content, and collaboration is important as this pool of libraries and users is more likely to have the time and funds to do such an endeavor as a practical 'second life' library community.