What version of Pro?
8GB works but there are a few know issues on older models
You have 2 options above 4GB:
8GB (2x4GB) (Usable on newer Unibody systems)
- Only the Santa Rosa and Penryn (MacBook (Pro) 3,1 and 4,1) can support 8GB memory. The MacBook (Pro) 2,1 only supports up to 3.25GB RAM accessible so adding in 8GB wouldn't matter since you can only access <4GB.
Update: New MacBook Pro(s) can support 8GB. As of September 2, 2009, the following 15" systems support 8GB ram:
MB985*/A – 15” Unibody MacBook Pro, Mid Range 2.66GHz (Dual Video Card)
MB986*/A – 15” Unibody MacBook Pro, High Range 2.8GHz (Dual Video Card)
MC026*/A – 15” Unibody MacBook Pro, Early 2009 2.66GHz (Dual Video Card) Note: This has not been confirmed