I switched over to 64 bit and am pretty happy overall. The one caveat is that a lot of plugins haven't switched over to 64 bit mode so you have to use this "audio unit bridge" to use them. It seems to work ok but you do take a bit of a performance hit. All things considered I think it's worth the hassle to have access to all my ram and logic is working well in 64 bit mode.
Here's some good books for Logic 9:
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