Now things have altered and you can use credit cards but more usefully, you can now book in advance. This applies not only to transport but also for all tourist services like museums. This is a real boon given the long queues that exist in the peak months. The problem with Venice is that there aren’t many times when it isn’t peak time. Tourists come throughout the year and those off months tend to be when the weather leads to the possibility of low level flooding and the wooden walkways come out. (Personally, I go when the carnival is over in February or towards the end of the Biennale -the art exhibition- in October. Then I can usually afford a hotel on the Grand Canal. Any other time and I stay on the Lido.)
So being able to book in advance, use a credit card and avoid the queues pleases me. The website to use is www.veniceconnected.it. There is one proviso. You must book 15 days in advance to be able to use the service so it isn’t for those who leave things or plan things at the last minute.