We very much enjoyed our stay at Marco's apartment in San Polo. The unit was very clean and in fact looks even nicer in person than in the pictures. It was very close to a number of restaurants, stores, and most importantly for us: a small supermarket where we could purchase a few goods for the apartment in order to save money and time on breakfast most days.
It's very nicely situated in the center of San Polo: heading in one direction takes you to the Rialto bridge (about a 5-10 minute walk as long as you don't get sidetracked by the numerous shops along the way) and heading in the other direction takes you towards the much quainter neighborhood of Dorsoduro (about a 10-15 minute walk) that is far less trafficked by tourists and overall a much more enjoyable place to be than the souvenir shop laden district of San Marco. Overall, San Polo gives someone visiting the best of both worlds of Venice: access to the more touristy districts as well as the more authentic and peaceful places frequented by those who call the lovely city of Venice home.
It was very helpful to have Marco meet us at the Alilaguna (water bus) stop but I think it's important to mention that there are a number of stairs across canals to navigate from the San Stae stop to the apartment. As long as you are not arriving midday, it may make more sense to go to the Rialto stop as there are only the steps on the one bridge to navigate and then beyond that it is a rather flat journey.
Overall - this was a great experience and as long as you are okay with carrying luggage up and down a few steps from either of the major transit stops in proximity to the apartment I would recommend this place to anyone.