I have been annoyed for over twelve months by a niggling performance issue on my laptop. My machine is a $4,000, gaming-spec'd beast (okay, from 2006, so it's not quite cutting edge), and I've been disappointed by the poor framerate and responsiveness I was getting out of it. Framerate in games was often (but not consistently) poor, quite often the mouse pointer would be jerky, and the keyboard would miss keystrokes, making it a frustrating experience even when simply typing in Word. I have tried so many things to try to remedy this I couldn't begin to explain it. I've been extremely careful in not loading it down with unnecessary software, so was really frustrated at what was obviously a software issue, but Toshiba couldn't help, and nothing I could find online was cutting the mustard. I'd spend days trying one remotely-plausible fix or another, give up in frustration, but have to try again after a while because using it was just so awful and I was convinced there would be a simple explanation for it somehow.
Then I stumbled across the TweakGuides Tweaking Companion.
The performance boost I've gotten from following some of the recommendations in the TGTC is nothing short of stupendous. The Toshiba is extremely responsive now, I'm getting framerates of 40-50 fps in NWN2, and my boost-up time has reduced from over a minute to 34 seconds! It's a dream to use now. I'm in lurve with my machine all over again. I cannot recommend this guide highly enough.
If you're at all dissatisfied with your system's performance, then give it a good go. It's the only resource I've found that has made any substantial difference in performance and responsiveness, and that difference has been profound. Even if you are happy with your comp's performance, give it a go - you could get more out your machine than you realise.
It's written clearly in plain English, explains the terminology it uses, clearly flags any tweaks that carry any risk of harming your system, and is utterly comprehensive. I'm a bit of a techno-geek - wholly unqualified, but an interested layman - and I was quite comfortable with it. It's a big document, but it's not necessary to follow it slavishly through from start to end to get benefits from it - I only applied some tweaks from about halfway through onwards, mostly because I know my system BIOS and drivers were up to date (that's the first piece of advice you get on the net when looking for performance improvements, and it had done bugger-all for me).
Go on. Try it. Your computer will love you for it and will definitely not want to kill you.
Oh, and I think the basic cause of my performance issues (yeah yeah, keep your mind out of the gutter!) was the Windows Indexing Service. The comp would slow down every time it accessed the hard drive, and the Indexer would be using the drive almost constantly. Not no more. Happy happy happy happy!