It is essential setting to be able to restore at least app data across incompatible ROMs.
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Thanks to pawitp the device is already ready for the forthcomming years.
His CM9.1 was the first masterpiece and CM11 is even better.
IMHO all CM10.x work excellent, just the codes of the JB roms drain bit too fast slim i9000's battery.
And very few people seem to know the very last official Samsungs GB update: JW9 that works just amazing and reminds rather on ICS roms than 2.x. It is much better than smooth but still quite slow JW4.
If somebody wants to try or save JW9, here is I9000XWJW9_I9000OXAJW4_I9000XWJW1 download link, it has multi-CSC (open Europe) and it isn't branded or filled with crap like Portugal's edition
This stock ROM really flies if you flash SpeedMod kernel k17-3 on it: under advanced SpeedMod options in CMW recovery (SpeedMod features CWM 126.96.36.199 it has "root / install SU" option)