The fifth major update to Mac OS X, Leopard, contains such a mountain of features - more than 300 by Apple's count -- that it's difficult to boil this $158 operating system release down to a few easy bullet points. Leopard is, at once, a major alteration to the Mac interface, a sweeping update to numerous included productivity programs, a serious attempt to improve Mac OS security, and a vast collection of tweaks and fixes scattered throughout every nook and cranny of the operating system.

As with every OS X update since version 10.1, there's no single feature in Leopard that will force Mac users to upgrade immediately. Instead, it's the sheer deluge of new features that's likely to persuade most active Mac users to upgrade, especially since this is the longest gap between OS X upgrades -- two and a half years -- since the product was introduced. Sure, some items on Apple's list of 300 features might seem inconsequential, but if even a handful of them hit you where you live, that will be more than enough motivation for you to upgrade.

A new look

Apple trumpets the interface changes in Leopard as "stunning" and "eye-opening", but in reality the changes are a mixed bag.

First, the good stuff: After years of experimenting with different looks for windows, sidebars, and other interface elements, Apple seems to have settled on a fairly consistent interface. The colour scheme is largely monochromatic-shades of grey with slight gradients. Apple has improved the contrast between the front most window and the rest of them by increasing the top window's drop shadow and dramatically lightening the colour of inactive windows. The Leopard Finder's new sidebar, clearly modelled after the iTunes Source List, is better organised and more usable than its Tiger counterpart.

Unfortunately, some of the changes are not as successful. The Mac's trademark menu bar, which spans the top of the screen, has been made semi-transparent. When the desktop is set to display an image with both light and dark areas, the see-through menu bar is visually striking. Unfortunately, that aesthetic choice comes at too steep a price: the areas of light and dark behind the menu bar can severely decrease the readability of menu items.

Apple has modified the Dock, OS X's built-in program launcher, so that the Dock's icons appear to sit on a reflective glass tray when the Dock is positioned on the bottom of the screen. (Someone must've pointed out to Apple that the metaphor broke down when the Dock is placed on the sides of the screen; in those orientations, the Dock's background is a simple half-transparent grey.) A pleasant glowing light appears next to the icons of currently-running programs, although the light is a bit too subtle when the Dock is positioned at the bottom of the screen.

Unfortunately, the Dock's new Stacks feature is a mess, replacing a utilitarian approach to stashing folders in the Dock (click to open the folder, click and hold to see a list of the folder's contents) with a snazzy but generally less useful pop-up window featuring a stack or grid of icons. A potential feature touted during earlier demonstrations of Leopard -- the ability to drag an arbitrary collection of items into the dock to make a temporary stack -- apparently didn't make it to the final version.