The Finder's Go > "Go to Folder..." (Shift-Command-G) menu item is a nifty way to access your file system.
First of all, you can use it to see hidden folders, so if you need to view /private/var, you don't have to open a Terminal window to do so.
Secondly, the "Go to Folder" window is an excellent place to paste a path rather than clicking around to get to a deeply nested folder. I use this pretty often when I'm troubleshooting. After all, if Apple's support documentation tells you to open ~/Library/Mail/V2/MailData to access a file within it, it's very quick to just copy that path and paste it into the window.
To make typing stuff in even faster, the "Go to Folder" window allows tab completion (just as Terminal does), and it tries to autofill as you type, as well. So if you type in ~/Doc and then wait for a moment, your Mac will attempt to figure out the destination and fill it in for you.
Important to note is that you aren't just limited to using "Go to Folder" within the Finder itself. The same keyboard shortcut can be used to invoke it within Open/Save dialogs, too.