Some of these comments seem a bit harsh to me.

I have been tweaking Mac for years without ill effects and I have lots of fun doing so. It's not everyone's cup of tea mind and if it's your one and only mac I would not! Always back up before tweaking so you can rebuild if it does not work. As for Speed, it's relative but you can expect a 40% increase if you methodically go through and delete 'start up items you can do without. For me that's Spotlight, Dashboard and Bluetooth that hog system resources. Apple does not recommend you 'customise' your Mac. Use a spare Mac and practice on that, not on your new piece of kit. For more osx tips see my weblink. Tiger needs some slimming pills to make it usable is my humble opinion.