Where does the Binding of Isaac store its saved data?
The game's save data is contained in two files, both of which need to be moved between computers in order to get everything migrated properly.
These files are so.sol and serial.txt. I have a Mac and a Windows machine, so I'll go ahead and list the location of said files on both platforms (if anyone has any Linux info, feel free to chip in).
On the PC:
serial.txt: Can be found in the game's steam installation folder, something along the lines of
C:\Program Files\Steam\SteamApps\common\the binding of isaac\
so.sol: Can be found over at
%appdata%\Macromedia\Flash Player\#SharedObjects\<some random string>\localhost\
The "random string" bit is some combination of letters and numbers which is impossible to predict. Assuming you've ever run the game, simply search for "so.sol" at "%appdata%\Macromedia\Flash Player#SharedObjects" (you can type this in your run prompt to get there). On my machine I have several so.sol files, but only one is on a path that looks exactly like the one I specified, and that's the one that counts.
On the Mac:
serial.txt: Can be found in the game's steam installation folder, something along the lines of
~/Library/Application Support/Steam/SteamApps/common/the binding of isaac/
so.sol: Much like the PC, only over at
~/Library/Preferences/Macromedia/Flash Player/#SharedObjects/<some random string>/localhost/
As a final note, I will stress again that you need to move both files, and that you need to launch the game at least once on the target machine to know where they should go.
The Binding of Issac cannot support steam cloud as it is a flash game and is not allowed to access the local filesystem except for using per site storage (or local shared objects, see http://en.wikipedia.org/wiki/Local_shared_object). It is impossible for the game to use steam cloud while it is running in the flash player (as opposed to AIR or some other language).
Just chiming in that for the Linux version, so.sol lives in:
~/.macromedia/Flash_Player/#SharedObjects/<random string>/localhost/so.sol
I do not appear to have a serial.txt file. I'm using the Humble Bundle version, not the Steam one, which is probably related.