My advice would concern accommodation issues. St.Petersburg is a big city with numeorus hotels, motels, flars to rent etc..the hotels are not cheap.... but! Don't even think of saving money by staying on the outskirts! One should think over how to save time in order to see at least half of "must see"! So my advice is to stay in the city centre - that is from Ploschad Vosstania (Moscowsky railway) along Nevsky prospect till Palace square. My hotels tips:
www.grandhoteleurope.com - premier 5-star hotel with antique furniture and fully equipped with all mod-cons, pretty penny
petropalacehotel.com - 4*, super location near St.Isaac's cathedral, but the service is average
silverhotel.ru - small, but very English hotel for 70 euro per night (I stayed in May 2011)
Hotels on Nevsky - chain of mini-hotels, moderate rates for good quality lodging, would recommend!
en.friendsplace.ru - no stars, hostel chain - cool, clean and cheap! would recommend as well!
Ra group - never ever