A few basic assumptions that help these itineraries fit most (but certainly not all) needs and styles
Every vacation is different, everybody has different needs, and nobody is starting off on the same page.
That said, in order to make itineraries that will as useful to as many people as possible, I am going to have to make some (probably wildly inaccurate) assumptions that will, hopefully, fit as many standard cases as possible.
For example, I am going to assume you want to spend as much time as possible on your vacation. That means leaving for your trip after work on Friday and not coming home until the last possible moment before you have to return to work—wouldn't you rather be jet-lagged and tired at work on Monday in order to max your time in Italy? If not, carve a day out of any of these itineraries so you can return a day early to unpack and recuperate.
I'm assuming that you're flying to Rome from North America. You may very well be coming from Australia (or wherever), or already be in Europe, and you may be flying into Milan or some other city. If so, alter things accordingly—which should be really easy, since, in most cases, you'll have a bit more at your disposal time than I'm allowing for here.
One giant assumption being made (at least in the general itineraries) is that you've never been to Italy before and what you want to see are all the major sights in the major destinations. While we have many variations on this theme (for example, some focus more time on Rome, others on southern Italy), the whole point is to help you fit in as much as possible of the big-ticket items.
These general itineraries will focus on the major sights—the major museums and churches of Rome, Florence, and Venice; the hiltowns and wines of Tuscany and Umbria; the Amalfi Coast and Cinque Terre, etc.—leavened with plenty of fun of offbeat things you didn't even know existed along the way. Still, they're going to maximize the major destinations and big ticket sights.
I'm also going to assume that, when you take a week off work for vacation, you are taking of Monday to Friday. You may very well have a trip planned for Tuesday-to-Tuesday. If so, you'll have to nip and tuck these itineraries, since the Mon–Fri crowd actually manage to finagle an extra day of vacation.