stolen from:

Keeping TRIM on Snow Leopard 10.6.8 Update

cd /System/Library/Extensions/IOAHCIFamily.kext\
/Contents/PlugIns/IOAHCIBlockStorage.kext/Contents/MacOS/

sudo cp -pX IOAHCIBlockStorage ~IOAHCIBlockStorage

sudo perl -pi -e \
‘s|\x41\x50\x50\x4c\x45\x20\x53\x53\x44|\x00\x00\x00\x00\x00\x00\x00\x00\x00|g’ \
IOAHCIBlockStorage

sudo rm /System/Library/Caches/com.apple.kext.caches/Startup/Extensions.mkext

sudo touch /System/Library/Extensions/

>> Maintenance, etc.. reboot and it should work