Today I upgraded the RAM of my MacBook Pro mid-2012 to 2x8GB. I purchased the Crucial 16GB Kit (8GBx2) DDR3/DDR3L 1600 MHz (PC3-12800) CL11 SODIMM 204-Pin 1.35V/1.5V Memory for Mac CT2K8G3S160BM from Amazon, which cost me $146.64 after tax. I followed the official guide as well as the iFixit guide. To finish the job I needed a Phillips #00 screwdriver and a spudger, so I purchased the spudger and the 54 bit driver kit from iFixit.
The actual process was pretty simple. I had a little bit of hard time pulling out the bottom module and pushing in the top module, but overall it was smooth. The only stupid thing I did was that I forgot to push the battery connector back in before I closed the case; I only realized this when I was screwing in the eighth screw (that was a close one!), and had to unscrew everything again.
After I replaced the RAM modules, booting was just normal. And now I've got 16 gigs of RAM!
Want to run multiple memory hoggers along with a Windows VM (with 4GB of RAM)? No problem.
By the way, Yosemite is indeed really aggressive at RAM usage. I reserve my opinion on whether there's a memory leak. But so far the performance has been fine, even with 8GB of RAM.