You can copy the apps to the SD with move to sd option in settings. It's not like it was on android <2.2. I'm not using ext partition sinds android 2.2/3 i always move the games to sd.
right now it's useless to keep the ext3 partition for the arc. because it isn't supporting apps2sd you have to wait for custom roms.
Samsung Galaxy S II
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Phone History (old to new):
Nokia 5110, Nokia 8850, Nokia 8210, Nokia 3310, Nokia 8310, Nokia 5210, Nokia 8910, Nokia 3410, Nokia 7650, Motorola V70, Sony CMD J7, SE T610, Nokia N-gage, Nokia 6230, Nokia 6230i, Siemens SL65, Siemens C65, SE K750, Nokia n73, SE K800, HTC Touch, HTC Touch Dual, HTC TytnII, SE Xperia x1, SE 303i, I-mate SPL, HTC Hero, NexusOne, SE X10, HTC WildFire, SE Xperia Arc