I regularly use Mac, Windows, and Linux. According to the
wiki, any backup files become unsafe to use after 100 new transactions. Barring that, where is my wallet stored? I imagine
C:\Users\<name>\AppData\Local\Bitcoin for Windows and
~/.bitcoin for Mac/Linux, but I'm not sure.
If I drag and drop my wallet from one OS to another, will the Bitcoin app recognize it, or is the wallet stored in a per-OS format?