The most significant change to the Common Application in recent years is the word limit on the personal essay. Before 2011, your own best judgment determined the essay length. Starting in the 2011 - 2012 admissions cycle, the application changed to state that the essay must be 250 to 500 words. That's not a lot of space in which to convey your passions and personality, although as Eileen's essay demonstrates, a strong writer can do a lot with fewer than 500 words.
I've had many applicants email me asking if the 500-word limit is enforced by the Common Application, and if they can go over the limit. The actual Common Application form has you upload your essay from your computer, and the software then converts your essay to a pdf file. The software does not count words or prevent you from submitting an essay that is longer than 500 words. That said, don't do it. While most colleges probably wouldn't even notice if your essay was 510 words long, you'd be wise to get rid of those 10 extra words. The strongest college students know how to follow directions, and the strongest writers know how to cut out all but the most essential elements of their essays. Show colleges that you can do both of these things.
The Common Application moved to the 500-word limit after lots of college admissions officers complained about long, rambling, poorly edited essays. Not all schools agreed with the limit. However, if a college wants more writing from you, they will ask for it with a supplemental essay. Don't try to second guess whether or not a college cares about the 500-word limit. Keep your personal essay short. Learn more in this article on essay length.