If you had a previous "android / google" device, I think all that information is kept at google.
I use a Droid Bionic and then bought a Nexus tablet. When I set it up at work I didnt give it much thought, connected it to the network (during setup). But when I got home, it already knew my router and password. HOW CONVIENENT... until I realized that it had ALL of my wifi connections listed.. NOW ITS SCARY!..