Xupport is another good option for people who want to optimize and fiddle with specific and global settings on their Macs. This multipurpose utility (billed as a "Swiss Army knife" for OS X) can help you navigate files, perform backups, search for Unix commands, and alter a wide array of settings on your Mac, all within a simple interface that's organized around Settings, Maintenance, Optimization, Sharing, Backup, Browser, Unix, and Info. Recent updates bring full support for Snow Leopard (important for a system-tinkering app), better stability for PPC Macs, and better performance for Intel Macs.
You can do everything from modifying the appearance of the Dock (gold indicators against a black background to show that an app is running, neat!) to optimizing your Internet connection, running system maintenance tasks (like fixing permissions and updating prebindings), and creating a bootable backup of your system disk. As with all applications of this sort, it's possible to do more harm than good, but Xupport is among your better choices for limiting potential havoc-wreaking, if you're worried about getting in over your head. The one downside to Xupport is that there are free apps that offer much of the same functionality.