Yes I know you know that this thing has been around since 2007 and people hated it because tons of reviews said they hated it and because buying 512MB more actual RAM gave actual more actual performance actually.
But I don't care about what all the numbers say. It's 2013 and the numbers from 2007 ain't mean anything. I have a 2009 laptop with 2GB of RAM and it slows down like a turtle when stuff have filled up the physical RAM and the laptop HDD is like a turtle pretending to be a snail. Enabling ReadyBoost with a Sandisk Cruzer Ultra 16GB with 4GB (the max allowed) for ReadyBoost cache prevented waiting for two minutes to switch between Photoshop and Foxit Reader and between multi-tabbed windows of Firefox. Yea, you know Firefox eats lots of memory per tab and will throw that thing onto the HDD so when you return to it later it loads from the HDD and you wait 15 minutes. You know that.
That's the thing. Some of this kind of performance increase cannot be measured by the usual numbers that we see. In the first place a properly-functioning computer wouldn't be lagging like that, and if it has 100MB/s of read speed it wouldn't be lagging like that even with all the spyware in the world. Fact - it isn't properly-functioning and does not have 100MB/s of read speed. So the posted numbers mean jack.
It's quite easy to spot HDD-related slowdowns. It is the only slowdown you get nowadays that lasts for more than 20ms. Mouse totally responsive, but window stays busy and unresponsive for simple things like web surfing and opening folders and Control Panel. Just plug in a flash storage media and see if it improves things.