Using this method, size and loading times are ( most likely ) not a problem. Have the user already done a hit on a page using this method before it will be in their cache.

Now somebody might say that it’s bad to rely entirely on Google; If the ( most unlikely ) event happens and Google fails to serve those scripts you can do it yourself like this:
if(typeof($)==’undefined’){document.write(”);

And finally, it actually really surprises me that you finds that most people don’t use the many functions of prototype when included :-O

For simpler things I write the code with plain JavaScript. For more complex task, I really enjoy prototype-js framework.

Well, now I’m gonna write a Movie player with subtext, using script.aculo.us, prototype-js and SoundManger 2 ;D

you example is flawed:
$(’someDiv’).style.display = ‘block’;
$(’someDiv’).style.top = ‘10px’;
$(’someDiv’).style.left = ‘10px’;

this can be written as:
$(’someDiv’).setStyle({display: ‘block’, top: ‘10px’, left: ‘10px’});

which is much more elegant.

see http://prototypejs.org/api/element/setStyle

If the answer is ‘none’, then that is an over-simplified example for which prototype is not intended.

How about giving an example on the scale of, say, Facebook.