Seriously guys, this is a great place to stay. Not only because the staff is making you feel welcome from the moment to enter the place. But because the go above and beyond to help you out whenever you need help.
Just one example: I forgot my passport in a small no-name coffee place in Iwangorod (about 400kms away from St. Petersburg). I only realized that when I arrived at the Rossi. The reception guys (headed by Maria) went on an investigation on Google Maps to find out what place it could have been, and since there was no phone number, they contacted the owner via the Russian facebook (who really kept all the documents safe and sound for me). Then they organized a driver to get the papers back to me within 24hrs whilst I was able to not loosing one hour of my time in St. Petersburg. When we were running late for our ferry on the last day, they rushed our backpacks to the port and instructed us (on the phone!) on how to maneuver most efficiently through the rush hour traffic so in the end we were able to board the ship on a last-minute basis... All that with a friendliness and effectiveness I have never seen before in a Hotel.
Besides the staff being diamonds, the place itself is pretty awesome, too. Exposed brick walls, designer lighting, a very cozy Spa area with a whirlpool, Hammam and Sauna. Everything is very well kept and one can see the love for every piece of Design that was added to the individual room. We've had a room on the 5th floor with a view on the river, which was pretty exceptional and bright and came along with a great rain forest shower in the bathroom.
Last but not least, the location is very central, close to the Nevsky Prospect and the Gostiny Dwor Metro Station. One can easily walk to all major Old Town Sights within 15-20 minutes.
I would recommend this place to anyone, and will be back myself in Summer for the White Nights.