Registered at the local library here in Purley today. Was quite easy, just had to take 2 utility bills along and they did the card right there and then.
Had to go through a 5 minute lecture on the rules, late fees and such. The kind lady then handed some papers to me to summarise all that she had gone through and said "This will tell you everything that I've gone through as you have forgotten it all by now anyway" - how well she knows me :-)
Found out that I can actually search the Croydon library catalogue online via Telnet. I was most impressed with that as you don't need to go out to them to check if they have something. A few clicks and you can see what library it's at and if its been taken out or not.