Academics collect library cards in the same way that compulsive shoppers accumulate credit cards. I have only seven or eight (library cards, not credit cards) but then I'm only a graduate student. My latest is the London Library in St James's Square.
I joined because I needed books at home to complete my PhD thesis that usually only reside on reference shelves. The London Library has a relatively small reference collection and almost everything else is borrowable. They also let you hang onto a book for as long as nobody else wants it, as long as you renew it regularly online. I have been correcting my thesis today and having the books to hand has been extremely useful. Thus, I felt that the London Library deserved a little plug here. It is kitted out like a Gentleman's Club (although it has no restrictions on membership) in a beautiful old building in the heart of clubland. They have a million or more books and presently they are almost doubling their size with a new extension.
There are only two drawbacks. One is a rather hefty membership fee (with no allowances for academics). The other is the metal stacks which can give you a serious electric shock if as you brush against them. But overall, I found it an excellent place to work and fantastic resource.
Comments or questions? Post them at Bede's dedicated yahoo group.