Hey Sarah,
I was a Vacation Planner at the TTC for the Summer of 2010, arguably the most stressful season at the most stressful park. However, it was the easiest and most amazing experience of my life. The training process is longer that most roles, about a week in the classroom learning the computer system, sales process, and every possible transaction you can think of. Once you get to your location, there is a great system in place to help new Vacation Planners hone their skills.
Yes, there is a sales incentive program (tickets have 'point' values associated, if you meet or exceed weekly levels, you are eligible for monthly prizes that range from gift cards to free resort stays). My experience with this was very positive. There are two types of Vacation Planners, those who stress and try and squeeze every dime out of guests, and those who just want to help the guest by the ticket they will actually need and use, because lets face it, Disney Parks sell themselves. I was one of the latter, I didn't concern myself with the sales incentives and point values, I just focused on my guests, turned out I was the top seller most days in July when the parks were the busiest. If you do not meet the goals, they have Cast Members whose sole role is to help develop you in the sales process. They not only assist the Vacation Planners, but our Cast that work in the Disney Reservation Centers.
As far as hours go, yes,they have better hours than most other roles. A downside though, is that shifts are usually 6 hours. There are opportunities for OT by working as a Park Greeter and helping with PAC (Parade Audience Control) if you are statused to the TTC.
My CP in this role I would say helped catapault me into my current career with the Company, you learn how to interact with people from all over the world, not to mention to Disney Ticket segment, which will help you if you want to get into Guest Relations or Resort Concierge after your program. Talk with your managers early on and let them know what your goals are during your program. Many VP managers came from other Lines of Business and can help you network.
What will make you the most successful in the role will be going to the parks in your off time. Part of the 'sales process' is selling guests on the parks and what you can do inside each of them. Learn what you like, learn what other types of people would like. How would a family with infant kids enjoy the parks versus a Dad and 15 year old son?
Hope this helps!