Since I havent done APEX, I cant say much about it. However, regarding EXCEL, I have lots to say...
It is definitely worth it. There is no doubt in my mind. Every other student that is currently doing it (40+) would say the same thing. First off, you learn the city of Boston and become comfortable getting around, using the bus and the T. You get a good feel for the city and wont need time later to adjust. Secondly, you meet over a third of your class. When school starts, we already have our core group of friends. For the most part, every one of us seems to get along with the others. Socially speaking, its a huge edge. Thirdly, and most important, you get tossed into the fire in regards to school work. Your days generally run from 8-5, similar to how it will be when "real" school starts. Also, you get a good feel of what it will take to be successful with the school work. You get an idea of just how much work is required to do well. Plus, you get a taste of how the exams are given during the school year. You also get yourself in a position where the faculty recognizes you, which could be beneficial later. Basically, when school begins, we wont be new to the process. The adjustment we will face will be minimal when compared to others who did not go through the process.
Now, Im not saying this to tell the other people that they are screwed. Not at all. Its just that I feel that EXCEL is very beneficial based on what I have seen. I think I speak for everyone in EXCEL when I say that the program is 100% worth it.
Maybe DB#1 can toss out his opinion as well, because maybe my analysis was completely off and I was talking out of my a$$.