Just for the record, I updated my 2009 MBP 13" from 4GB of RAM to 8GB of RAM. From the factory it was spec'ed to have a maximum of 4GB, but somewhere along the road Apple updated the BIOS/EFI to allow 8. Maybe it was around the release of Lion, but as long as you have it you are ready. It wasn't trouble free for me as I initially purchased two 4GB 1333MHz DD3 from Crucial thinking the Mac would underclock them to the specified 1066MHz. Nope. Multiple hard-as-a-rock crashes, not even a blue screen or grey screen or reboot, just stopped. Windows via Bootcamp would start and run for a bit at 1333MHz, but MacOS wouldn't even get close. Swapped them SODIMMs out for 1066MHz parts and everything was great. I've had a two hard freezes since the upgrade, but not sure if it is x64 compatibility with some of my engineering hardware drivers or what.
I really wanted an SSD for the laptop, but I needed at least 500GB which was just too much money for now, so I found a Seagate Momentous 750GB Hybrid drive on Amazon. It is a 7200RPM laptop hard drive with an 8GB SSD buffer integrated, with 32MB of RAM buffer, too. I found it for just $20 more than a regular 750GB so I went for it. Turns out it was a good choice! Loading the operating systems and dev tools is very noticeably faster, and I was coming from a Western Digital Scorpio Black 320GB 7200RPM drive. Since then I read some reviews at Gizmodo and Anandtech and my feelings were confirmed by their benchmarks. Sometimes you get SSD performance and sometimes you are limited by the spinning platters but still get performance as good as a high end desktop disk. I'm so happy I ordered another one for my 2007 iMac because I'm tired of hearing the factory 3.5" drive churn and I'm pretty sure it'll breath new life in to the ol' girl.
Love the upgrade still, the initial freezes must have been unrelated. Everything is great working the old computer to death with Mountain Lion, Parallels 7, and Windows 7 x64. My wife's new Core i7 MacBook Air with 8GB of RAM and 512GB SSD is making me look kinda dumb now though.