It is difficult to speak of the benefits or detractions of Web 2.0 applications in an abstract and theoretical way as I believe that their success or failure is greatly depended on the context of the library: it’s user base, the services its promoting, the other resources available etc.

I think it’s been stated ad nauseum, but it bears repeating, that the key to the success of social software depends on the library itself reaching out to the community (or whatever their base might be), understanding their needs and expectations. Ultimately social software is merely a means of improving an already communication in an already existing relationship between patrons and the library and not something to act in lieu of other forms of interaction.

I think that the main advantage of most of the social software applications (with the exception of social bookmarking in my opinion), is that the cost of failure is relatively low. I don’t think that any application requires an enormous amount of technical knowledge, staff time or money. That’s not to say that a library shouldn’t do research and planning before any kind of implementation but there really is no way of knowing whether what you do will take off or not except by experimenting and putting it out there.