Years ago we stayed a few nights at the former Courtyard (Holiday Inn now I think), and took the shuttle bus to the parks. At that time the bus service was about 1 bus per hour, and only went to certain parks (next bus, next hour, different parks). The next year we stayed off site again (over near the convention center) and they had a free shuttle, but we preferred to drive and pay to park for being able to come and go on our schedule. The Disney bus system is superior to the offsite services, but that is typically reflected in the higher price you pay for onsite room rates. Tickets can be purchased at the gate, or online, either through Disney, or one of the authorized ticket sells.