It took me a while, but I've really grown enamored with the "column view" (the one with the side-by-side columns that all appear in the same window) in Finder windows in OS X. It's a relief not to have to continually open new windows to find what I want in my 60GB hard drive.

I like columns even more so these days, since I discovered how to navigate them via the keyboard instead of always having to drag the jellybean scrollbars around.

In addition to Finder windows, most of the same keyboard shortcuts I'll talk about also work in the OS X's Open/Save dialogs (technically they're called "sheets" now btw) which you may have noticed don't support any view of your hard drive's files other than column view.

Beginning/occasional web designers may have noticed that there's no easy way to add a custom-colored border around a .jpeg or .gif in their web page. Yes, you can set a border width attribute in the <img src> tag, for example:
<img src="logo.gif" border="5">
… but the color of the border is the default color of your body text, usually black. If the image is a link, the border changes color to match your link color. [Note: For brevity's sake I'm not including the image's alt, height or width attributes in these code examples, but they should of course be there.]