There is an old post from 2nd October 2006 about pre-booked water transfers which has unfortunately been suspended for further comment, because it exactly matches my very recent experience (6th September 2013).
"Two days before leaving we received [a message] which said the transfer would usually be by water taxi from the airport but the taxi firm could alter this to a car transfer to P Roma and water taxi from there to hotel....We were then transferred in a glorified van to P Roma, had a 10 min water taxi ride on the back canal, and were then dumped some distance from our hotel and we had to walk at least 800m to the hotel!"
In my case, it was slightly worse, because the 'taxi' was 30 minutes late and neither telephone number provided worked. When we complained to the 'airport representative', she said she was doing me a favour by calling another number! In my case, the culprit agency was venetoinside.com, although the voucher was from 'Itaiianescapade'.
Has anyone recently had the same experience, especially with one of these two agencies?