Mac OS X is easy to navigate. You can Command-Tab between applications or use Expose to see the desktop and switch between windows. (Do you ever use a Windows PC and find yourself moving the mouse cursor to the corners, only to get frustrated when nothing happens?)
And then there are 3rd party apps. Everyone I know who gets acclimated to Quicksilver never goes back.
VirtueDesktops gives you one more way to manage your workflow. It is a ?virtual desktop manager?, which helps you organize all your open windows. You can open up your Mail program in one ?desktop?, your word processing program and dictionary in another ?desktop?, and your Photoshop work in another ?desktop? and then switch between them. Each ?desktop? is kept separate from the others so when you want to switch tasks you don't have to close some windows and open the others.