Sure, Xcode is not the standard designers tool, but it might happen that you need to tweak an open source app, or that you want to build a frontend for one of your scripts. Either way, Xcode can be quite confusing, it took me some time to understand how to use it (I think it’s especially bad if ones comes from the VisualStudio background as things are really different there). OSNews lists some worthwhile Apple tutorials on Xcode, it’s a good read if you’re interested in this topic.
Link

This is a gooood link. Not much to say here; it’s a Adobe document describing how to improve Photoshop’s performance under Mac OS X (there’s a Windows version too :) ).
http://www.adobe.com/support/techdocs/317280.html

This is an awesome tip. I should have known about this some months ago when I sold my iBook. Theconsultant.net explains how to reset your Mac so it starts with the Out-Of-The-Box experience again, that is Intro-Movie, Account setup, Network-Setup, etc. I think that’s a great thing to do when you sell a Mac.

Macworld has a nice set of tips which help to get the most out of Safari. Although I knew some of those already the others were highly interesting.

I love the Mac OS X Tiger slideshow option. It’s the way to go if you need to review a certain set of images – quick.

It has a few drawbacks though, on the one hand it’s impossible to select several images while you’re reviewing them, and still have this selection active after you quite the slideshow (i.e. as a finder selection). And on the other hand, there’s the boring slideshow transition. It should use a cube transition here, the cube always enchants the audience.

Now you can at least change the 2. drawback. One can edit the transition-file using Apple’s Quartz Compmoser application. More Details here:

Edit Tiger’s slideshow transitions – The Unofficial Apple Weblog (TUAW)