I did this party last year and it was lots of fun. On the day I did it, the "dessert party" portion was held inside at Liberty Tree Tavern, where you had your selection of specialty desserts and did the meet & greet with Tiana and Naveen. Then they escorted us over to the boat, which traveled around the river and stopped up near Frontierland by the start of the parade for the viewing. You can stake out a position on any of the three levels of the boat to get a view of the parade (in general, the higher you go, the better you'll be able to see).
During the parade there were more desserts and drinks available on the boat, and Tiana and Naveen joined the onboard party after the initial trip around (but before the parade), and did their own little parade that the kids could join and continued doing more "candid" style meets with guests. As a big fan of princesses in general and "The Princess and the Frog" specifically, it was a great experience and well worth the money for me.