I have a mac mini. It is cool although you do not get an iSight with it! I hate it! However, your user pic can have special effects.
Pop open Address Book.app and click your user account entry and edit the picture, there should be a swirly icon that you can make an effect with your pic! (NOTE: This may not take effect until a reboot!)
Watch the video demo
I was just fooling around with the menubar in Finder when I found that if you press the ‘option’ key you get some different options. Try it. Click on the Apple (top left) to show the menu, then press “option”. Notice some items change? Try it on the other menu’s (file, edit, etc).
One cool trick, if you click the apple menu, then press option you will notice the dots disappear from some items. If you click the ’shutdown’ menu item the machine will shutdown without that pesky confirmation message. Neat!
Not exactly a power tip… so don’t rip me apart because I know this isn’t high tech. Do you get annoyed by cluttered post-it’s crowding your dashboard? (See below)
A lot of times you can’t read them easily and your eyes just miss them. But I’ve found a work-around. First, open up Text Edit or your favorite word processing app. Type your message there and increase font size as large as you like. I used 100pt in this example. 
Now, press down Shift + Command + 4 to take a selected screenshot of your text. The image will save to the desktop. Then drag the image to the Safari icon in the dock. A new tab will open up with your image in it. Now, take a web clip of the image. It’s that simple. Now you have an easy to read post-it.
For those of you who have lost your Apple Remote or have an older Mac without an IR reciever, the new and improved Front Row included with Leopard now has keyboard commands. You can start Front Row with the icon in the Applications folder, but you can also start it with Command (⌘) + ESC. From there, UP is equivalent to + on the remote and DOWN to - ; LEFT to rewind; RIGHT to fast forward; ENTER to pause/play; and ESC to menu. The keys work exactly the same as the buttons on the remote.
You can change the volume in iTunes in its minimised window form by hovering the mighty mouse over it and using the scroll ball. This works regardless of whether iTunes is the active window or not.
Make your mac stand out from the rest by customizing your log in screen!
Grab your favorite background image, save it as ‘background.jpg’ and execute the following from Terminal:
sudo cp background.jpg /System/Library/CoreServices/DefaultDesktop.jpg
(you need to be in the same directory as the background.jpg for the copy to work. Eg if it’s on your desktop then “cd ~/Desktop” to change to that directory first)
source: lifehacker.com.au
Press Control + T to swap the two characters before the cursor. Appel > Apple
I don’t consider myself very hip on mac tricks/haxies yet the ones I have been ready are straight from the Apple web page… here are a few terminal commands I use so often I never forget them. I’d love to know some more:
1. defaults write com.apple.Dock showhidden -bool YES (Makes hidden applications’ dock icons translucent. NO to reverse.)
2. killall (example “killall Dock”) basic… quick dock/dashboard reset
3. defaults write com.apple.dashboard devmode YES (unlocks dashboard dev mode.NO to reverse.)
4. defaults write com.apple.dock mouse-over-hilte-stack -boolean YES (highlight cursor in stacks)
5. defaults write com.apple.Dock workspaces-auto-swoosh -bool NO (disabled space switching for command-tab…YES to undo as with others)
