My experience is similar to daannzzz's. Some ride times can creep a little longer than 15 minutes, but if you use FastPass well, you can avoid standing for very long.
EMH is good for most parks, even Epcot. What my DW and I do is go to EMH, then hop to another park by mid-day. At Epcot, however, we usually spend the entire day and have never had problems with crowds.
We avoid MK on Saturdays like the plague -- unless you like being shoulder to shoulder with people all day long.
We usually made a PS for dinner if we ate in the parks; it saved some wait time at the restaurant. Lunch -- we played by ear. Never had a huge wait. Sometimes we'd make a last-minute PS at the park when we went in.