I stayed two nights at the Boutique San Marco, and I liked it a lot. The rooms are located in the third floor of a beautiful old palazzo only a few minutes away from the Piazza di San Marco, and from my room I had a nice view on the canal and could even see the bell tower of San Marco. The place is comfortable and clean, you can use the kitchen if you want to, and everybody's very nice.
In the evening you could hear boats cruising on the canal and in the morning it got a little noisy when the garbage boat was collecting trash (at least I think it was the garbage boat), but nevertheless I had a really good sleep, and next time I'll be in Venice I'd love to stay at Annette's again.