The waterboat service is another option that we've heard good things about. There are various pick up points around Venice, the tours office on the ship should have all the information but this link might help.
Have a lovely cruise & please bring some sunshine to London with you :o)
Alan & Katrina
Next Cruise: P&O Adonia - 20th May 2013
Last Cruise: Queen Victoria - Xmas/New Year
Golden, Grand(2), Caribbean, Sea(4+1 aborted)
Adonia(4), Arcadia, Artemis(2), Aurora(5), Azura, Oceana(3), Oriana(10), Ventura(2), Victoria(5)
QM2(2), QE2(9), QV(5), Caronia(2), Minerva II, Fred.Olsen(8), NCL Jade, =X= Eclipse, HAL Ryndam