What is the true value of a public library?

It seems that, in the UK at least, the public library is a service that constantly has to defend its right to exist. As Goulding has suggested, although public feeling towards libraries seems to remain positive, commentators, both political and social, like nothing more than to paint the picture of a service "at crisis point" (Goulding, 2006, p. 4). Yet from the outside looking in, so much of the navel-gazing instigated by such reports that cry the death knell of the public library, seem built on shaky foundations, and, it seems to me, a complete misunderstanding of what the public library concept is and how we should value it. More worryingly, the agendas created by such navel-gazing run the risk of weakening the service even further by encouraging a focus on issue statistics or other numbers-driven methodologies as the absolute guarantor of the potential value of a public library to its community and to society. So how should we measure the value of a public library? What indeed do we mean by value?