I had a fantastic stay at Silvia's place. Silvia is an excellent host and was always quick to respond to my queries before and during my stay. She was eager to make sure I was comfortable and had everything I needed. Her place is really close to the Accademia, which meant getting back after exploring was very easy (there are signs everywhere saying "All' Accademia" (to Accademia).
The room was very clean and had just what I needed for my stay. I didn't make much use of the nice secure courtyard outside, except to hang out a little bit of washing. The small lane was nice and quiet at night so I had no trouble sleeping.
I really appreciated being able to leave my bag in the secure entranceway before properly checking in. This meant I didn't have to pay to leave it at the train station, go and explore, then go back again to pick my bag up before going to Silvia's place.
One little tip for people - I made the foolish decision to walk from the train station to Silvia's place with a very big bag. I hadn't thought it through beforehand, but there are a lot of bridges to cross and none of them had ramps so I had to pick up my bag and carry it over each one. It would be fine if you had a small bag, or especially if you just had a backpack. Taking the Vaporetto is extremely easy so I would recommend that instead if you are like me and can't travel light!
In terms of location, walking to St Mark's Square is very easy - 15-25 mins away depending on how many photos you stop to take along the way. Download the Venice map on Google Maps so that you can use it offline. I found that very helpful if I ever got a bit lost. Silvia has a Rick Steves guidebook and map available for the use of her guests which could come in very handy.