@chemgeek - great tips. Decided to skip Venice?
Venice may or may not fit with your travel "style". If you're a "let's wander and get in adventures" type of traveler (like me), then you'll LOVE Venice. It's full of crooked walkways, back alleys, dead ends, and you'll pretty much be perpetually lost as it's one big maze. But hey, you're on an island, so it's not like you can really be too lost.
If you're more of a "we need to be here at this time" type of traveler, or "let's eat great food" type, then Venice can be frustrating. Venice is filled with tourist trap restaurants and the ones that aren't are ridiculously expensive. I'd recommend simple eating in Venice like pizza, panini, or finding the grocery store and buying picnic supplies.
We also did two weeks in June of 2012. Flew into Milan but didn't spend any time there as we went straight to Lake Como. From there to Venice, Florence, Cinque Terre, Siena, and Rome (flew home from Rome). It was slightly rushed, but I'm glad we got to see as much as we did. Probably could've covered all of that comfortably with only a couple of more days. Well, you could easily spend a week in Rome and barely touch it. Rome was amazing. Of course it wasn't a honeymoon trip like chemgeek above, so we were okay spending all day away from our room and collapsing into bed at night. :)
And if it wasn't mentioned upthread anywhere, get the Rick Steves Italy book. Rick is the man.
If you have specific questions, I'm happy to answer any you have on any of the above cities/areas if I can.