Crypton Future Media is the company that created the virtual Diva "Hatsune Miku". Crypton officer are located on the 11th floor in this building. It is a 5-minute walk south of the station.
You can visit and sign a guestbook and leave notes for the creators or other fans at the entrance to the office. Remember to keep the noise to a minimum as this is still an office building.
This is definitely a must visit for Vocaloid fans and not too far from the station. So if you do visit Sapporo you should visit!