I've been experiencing a very slow 15" Pro recently, images take ages to load off the hard disk (eg when switching from my built in display to an external one it takes about 2 minutes to reload the slightly bigger sized launchpad icons), it once took 10 minutes to boot and it cannot shut down without me quitting everything first. The Genius guys (who were really very helpful and nice about the situation, although I believe, wrong) advised me that because kernel_task was taking up too much RAM (600mb) that it was slowing my system down. It's the task using most of my real memory, the second being either Chrome or iTunes most of the time. They advised a fresh install of Lion. I've now done this, and I'm back where I started. Kernel_task is still running at 600mb. What's worse is that my hard disk appears to have slowed down. Previously it was writing/reading at about 50mb/s, now 40mb/s. It's a 5400rpm drive but still that is too slow, surely? Tl;dr: How much RAM should kernel_task use, what is the normal read/write speed on a 5400rpm drive? Or just: why is my computer slow? And believe me, when I have the money I will be getting an optibay. specs: 15" i7 at 2.0ghz, 4gb RAM, 500gb 5400rpm.