However, using this app directly is often a pain. You have to open it up, create a new session, type in the URL/IP, and then possibly authenticate. If you, like me, are accustomed to using Terminal for most of your tasks, there is an easier and quicker way: use the "open" command, which is built in to OSX.
From a standard shell, run open as in one of these examples:
open vnc://www.example.com
open vnc://111.111.111.111
open vnc://mylocalserver.local
If you often VNC into the same computer, you can create an alias in your shell's profile so you don't have to type the command every time. Combine this with QuickSilver, and you can open a VNC connection to the server of your choice in as little as 5 key-strokes!
[crarko adds: I tested this, and it works as described. This is an elaboration of an earlier hint.]

