I received shipment of a 16GB RAM kit from Crucial for my mid 2012 base 15in MBP. I was getting some beachballs and lags when a lot of stuff was open, and significant page outs. So now I was only able to get a millisecond beach ball by opening about 10 different programs at once. Everything opens slightly faster and it's just snappier. I hope it keeps up this way. Might be the best $100 I've spent in a long time. I really don't think 4GB is enough anymore if you are running several things at once (or are too lazy to close down stuff when you're done with it, like me). Well it's ENOUGH, but I think it's really the bare minimum you need to operate the system smoothly. Not saying you need 16GB either, but it was only 20 bucks more than 8GB, so I just went for it, and I'll never have to add RAM to this particular unit ever again. Will wait and see how far SSD prices drop in the next several months to make a decision about my next upgrade.