How can I get a high-quality screen capture on a mac? ⌘ + Shift + 3

The screen capture shortcut on the Mac is one of the most useful tools I know. It grabs the screen and neatly places a .png file onto your desktop.

But is this the highest quality screen capture you can get? Is it possible to get a higher resolution screen capture? Are there any ways to tinker with the settings of this command?
The PNG is losslessly compressed; there's isn't a possible better-quality screenshot.