What would be a stable OS upgrade for my mid/late 2007 Mac Book Pro?
I actually have the very same machine. I started with Snow Leopard, since it originally had 1GB of RAM. After a bit of playing, I decided I liked the newer UI better and upgraded to Lion. Lion is a LOT better on this machine, very snappy, and has support for newer software from the Mac App Store. Unfortunately, some pre-Unibody MacBooks CANNOT be upgraded past Lion without hacks. Main reason being the graphics unable to keep up with the later 'beauty' introduced into the operating system.