Looking around the web there's a bit of misinformation as to whether 8 gigs of ram will ever work in a 2008 MBP, not the 4gb Apple recommends or even 6gb max some sites recommend.
I have a late 2008 MBP 2.8ghz 4gb ram. I checked the Boot ROM Version in the System Profiler and it matched the version needed to upgrade to 8GB ram according to OWC (if it didn't there is a link to upgrade the EFI Firmware version. Also, my OS had already been upgraded to Snow Leopard which is also a requirement. I bought 8gb Crucial ram from Newegg on Black Friday for $49, now it's even CHEAPER, only $39! Followed the super easy instructions (blew out all the dust/dog hair inside) and wammo! The System profiler shows 8GB Memory and everything runs nice and snappy!
How to you ensure your MacBook/MacBook Pro can address 8GB of RAM
Check the Boot ROM Version in your System Profiler at this link:
MacBook Pros with a Model ID of MacBookPro5,1 should have a Boot ROM Version of MBP51.007E.B05.
MacBooks with a Model ID of MacBook5,1 should have a Boot ROM version of MB51.007D.B03
Machines with other Model IDs are not affected and don't need an update.
If your Boot ROM version does not match the numbers above, download the appropriate
For MacBook Pros (MacBookPro5,1)
MacBook Pro EFI Firmware Update 1.8 (Apple.com Download)
For MacBooks (MacBook5,1)
MacBook EFI Firmware Update 1.4 (Apple.com Download)
Once you have ensured that the Boot ROM is the correct version,
make sure your Operating System is updated to Mac OS X v10.6.6.
You must be running Snow Leopard to address 8GB on these systems.
MacBook, MacBook Pro
Newegg.com - Crucial 8GB (2 x 4GB) 204-Pin DDR3 SO-DIMM DDR3 1066 (PC3 8500) Laptop Memory Model CT2KIT51264BC1067
Installing MacBook Pro 15" Unibody Late 2008 and Early 2009 RAM - iFixit
I have a late 2008 MBP 2.8ghz 4gb ram. I checked the Boot ROM Version in the System Profiler and it matched the version needed to upgrade to 8GB ram according to OWC (if it didn't there is a link to upgrade the EFI Firmware version. Also, my OS had already been upgraded to Snow Leopard which is also a requirement. I bought 8gb Crucial ram from Newegg on Black Friday for $49, now it's even CHEAPER, only $39! Followed the super easy instructions (blew out all the dust/dog hair inside) and wammo! The System profiler shows 8GB Memory and everything runs nice and snappy!
How to you ensure your MacBook/MacBook Pro can address 8GB of RAM
Check the Boot ROM Version in your System Profiler at this link:
MacBook Pros with a Model ID of MacBookPro5,1 should have a Boot ROM Version of MBP51.007E.B05.
MacBooks with a Model ID of MacBook5,1 should have a Boot ROM version of MB51.007D.B03
Machines with other Model IDs are not affected and don't need an update.
If your Boot ROM version does not match the numbers above, download the appropriate
For MacBook Pros (MacBookPro5,1)
MacBook Pro EFI Firmware Update 1.8 (Apple.com Download)
For MacBooks (MacBook5,1)
MacBook EFI Firmware Update 1.4 (Apple.com Download)
Once you have ensured that the Boot ROM is the correct version,
make sure your Operating System is updated to Mac OS X v10.6.6.
You must be running Snow Leopard to address 8GB on these systems.
MacBook, MacBook Pro
Newegg.com - Crucial 8GB (2 x 4GB) 204-Pin DDR3 SO-DIMM DDR3 1066 (PC3 8500) Laptop Memory Model CT2KIT51264BC1067
Installing MacBook Pro 15" Unibody Late 2008 and Early 2009 RAM - iFixit