I can buy a whole new
ThinkPad with 16GB RAM for little more than that price of RAM!
I have a ThinkPad w520 with 16G memory in my lap right now. The cost of the memory through my employer was $33 per 4G or $132 total.
I asked for a 15" MacBook Pro but unfortunately needed 16G memory for my work - and the cost of the MBP shot to over $3500 by the time the memory was considered, ergo I got stuck with a ThinkPad. (My ThinkPad is a 2.2GHz i7 quad with a 1920x1080 monitor - so pound for pound it meets or beats the 15" MBP. It just doesn't run OS X, dang-it!)
I believe the ThinkPad can go up to 32G using 8G DIMMs, but that would be a pricey upgrade. Hopefully 8G DIMMs will be a lot cheaper by the time I'm ready for my next upgrade and I can go back to Mac.
Sam