Moreover, when you output a jQuery Object it will include a reference to that element in the DOM, and clicking it will go to that in the Elements/HTML tab.
You can use various methods, but beware that for it to work in Firefox, you must have Firebug open, otherwise the whole page will crash. Whether what you're logging is a variable, array, object or DOM element, it will give you a full breakdown including the prototype for the object as well (always interesting to have a poke around). You can also include as many arguments as you want, and they will be replaced by spaces.
console.log( myvar, "Logged!");
console.info( myvar, "Logged!");
console.warn( myvar, "Logged!");
These show up with different logos for each command.
You can also use
console.profile(profileName); to start profiling a function, script etc. And then end it with
console.profileEnd(profileName); and it will show up in you Profiles tab in Chrome (don't know with FF).
For a complete reference go to http://getfirebug.com/logging and I suggest you read it. (Traces, groups, profiling, object inspection).
Hope this helps!