This tip seems out of place since Equation Editor is pretty old and has been OS X compatible I since Appleworks 6 came out (I think). But since you brought it up, I'll mention a bit more about it and some other math formula programs, including one for learning algebra-calc step by step.

Equation Editor, which comes with Clarisworks 5/Appleworks 5 and Appleworks 6, also comes with MS Word 97(maybe even earlier than 97) and up (yes v.X has Equation Editor). It may also come with Corel WordPerfect 3.5 (the free version) because WordPerfect has an equation editor which looks nearly identical, but I couldn't find an 'About MathType' box so...anyway.
Its a toned down version of MathType and you can find more information and tips about it here:
http://www.mathtype.com/en/products/ee/index.asp

Equation Editor is quite nice and surprisingly powerful. I prefer the Appleworks version over the Office version because it runs as a separate program. It has shortcuts like apple-/ to create a fraction where you then enter the numerator and hit tab to enter the denominator and in the pre-OSX version apple-h was the shortcut for exponents or superscript, now it hides the app. Its quite versatile and I've made some nice math notecards with it.

But if you're really into editing equations here's some more programs you'll want to check out:

MathMagic Personal Edition (v. 3.0 is 30day trial and OS X native, versions 2.5 and earlier are Classic only but are free) http://www.mathmagic.com/
MathMagic also provides a profession version for Quark users and both versions can export to TeX
MathMagic has an interface very similar to Equation Editor with nearly identical shortcuts only it has more shortcuts and such.

OpenOffice --> the current version has a nice equation editor, similiar to Equation Editor, except the shortcuts are based on LaTeX macros.

I'm playing around with LaTeX currently, namely iTeXMac (Mac front end and editor with shortcuts to tex)

and texmacs (not actually tex and requires x-windows but displays everything as you type. Much easier to 'see' a fraction 2/3 than look at \frac{2}{3}

Not to get too far off the Equation Editor topic but I'll also plug a program called MathXpert for learning Algebra and pre-calculus and Calc I. It takes you through step by step, and it even allows you to go through the functions step by step deriving some archaic function. Its OS 9 and OS X compatible and there is even an online version developed using webobjects.
http://www.mathxpert.com