The Oktoberfest can be great fun, apart from all the beer and food there is a great Fairground with some amazing rides. I found it best to stay on the outskirts of Munich as the accommodation is cheaper. I reccomend Hotel Soller in Ismanning, directly opposite the S Bahn Station, great food and friendly service.
The Oktoberfest is great to see once in your life as a Tourist, but it can be quite expensive. Most of the seats in the Beer Tents are booked months in advance, but dont let that spoil the visit. Stroll round, enjoy the atmosphere and the fairground, the various snacks you can buy, it is unique. It is better to book a Hotel away from the City Centre where it will be a better price. We used the Soller in Ismanning which is just over the road from the S Bahn Station.