Android 4.4 on Galaxy S I9000 stuck at boot with ART
As "ART" versus "Dalvik" is a setting the user can switch, a factory-reset should restore its previous (default) state – in this case, revert it to "Dalvik". Reportedly, the following steps solved the issue in this case:


Complete wipe, including Dalvik Cache and data (can be done from recovery-mode, and is equivalent to a factory-reset)
Re-flashing the ROM (IMHO an optional step, as the previous one should suffice)


Remark: There's a good reason that switch is a little hidden; ART is still "experimental", and not intended for "everyday use". It was placed with the developer's options just to give developers a way to already test their apps for compatibility.