We are going on our honeymoon the first week of June but need to go through London. Please help me fill in a bit of our itinerary!
Night 1 London (fly to Venice 7 am the next day)
Night 2 Venice
Night 3 Venice
Night 4 Florence (taking the train)
Night 5 Florence
Nights 6, 7, 8 --- renting a car in Florence? Driving to CT? My fiance really wants to go to CT, but I've heard Bellagio is wonderful too.

We like the freedom of having a car and we don't mind changing hotels alot.
And we need to be in Pisa by 8 pm on Day 9 to catch our flight home.

I was in Como and Bellagio yesterday. Stunningly beautiful. I too had the same dilemma as you and after reading threads here and on other sites decided to give CT a miss. I had been to Como on a day trip 23 years ago but not Bellagio. I feel I made the right decision for me if thats any help to you!

The Pisa departure decides for you--do the CT.

We were in CT early April for our anniversary and found it very romantic. I am happy to provide any info you want and agree with Bob's comment.

I would say that you have two considerations:
#1 Room Availablility
#2 Weather (specifically Temperature)

We're head to Lake Como for early June and weather forecast looks fantastic (for Lake Como)

I would imagine the hotles at both places are filling up rapidly.

That sure sounds rushed for a honeymoon. I'd stay at least another night in Venice and Florence and then head to the CT for the final two nights.

My wife and I have been to CT and Bellagio and while we liked both, Bellagio and the lakes area are more scenic (at least in our opinion). Bob is correct though, to drive from Florence to Bellagio and then to Pisa for your flight home is too much. We drove from Bellagio to CT, and as I remember it was around 4 hours. The viamichelin site says Bellagio to Pisa is just under 4 hours but you need to factor in getting lost (we did) and other unknowns, traffic, etc. CT is very nice, we stayed in Santa Margherita at the Continental Hotel. From there you can catch the train to the villages along the coast and walk to Portofino, not to be missed. I take it your flight leaves on day 9 so you will need to arrive in Pisa early enough to check in at the airport.