We went once in early Feburary and had really bad luck. It is now referred to as "The Chicken Finger Trip" because everytime we wanted to eat something, we couldn't find someplace that could seat us quickly and ended up eating counter service.
A few things to keep in mind if you are going to try it.
1. Small parties are easier to seat than large parties.
2. Its easier to get seated at 4pm than at 6pm
3. In some places, sit down restaurants are few and far between. Even the World Showcase, restaurant central, it can be quite a walk from one restaurant to the next, which can be overwhelming if you are hungry.
4. If you really want to eat somewhere, make a PS.
5. Popular restaurants should have PSs year round. Some people have gotten incredibly lucky, but don't count on it. This includes all character meals, Boma, Le Cellier, Teppenyaki, several other restaurants in the World Showcase......
6. Know where good counter service is. Nothing worse than being starving at MGM to find all the sit down places booked solid and having no idea where to go for anything other than chicken fingers (WDW does have good chicken fingers, they just get old fast).
7. Start looking for food when you start to get hungry. You may have an hour wait or be turned away from your first several stops.