I'm a sophomore in MYP right now, and the classes so far aren't that difficult, though that may be because the Honors kids are mixed in ALL of our classes.
All of that changes next year, though. I am almost definitely continuing with DP (Diploma Program, the last two years of IB and the only two that really mean anything in my school district xD). I've asked a lot of people about it, from Traditional to Honors/AP to DP students and teachers as well. Honestly, most people in traditional (at my school) just don't try at all in their studies. So many people are in honors/AP/IB that it looks REALLY bad for the traditional students. General consensus is that if you're in DP, your life REALLY sucks :P; if you're in AP, you're average/normal (unless you're taking like more than four at once); if you're in Honors as an underclassman, you're normal/average but if you're in it as an upperclassmen, you're behind; and if you're in traditional, you're going to one of the community colleges less than 5 miles away (if even that). xD
In recent years, I feel like DP has gotten a much worse rap than it deserves. Sure, the workload sounds brutal and at times pointless, but almost everyone I've talked to has told me that IB prepares you so much better for college than AP. Even some of the AP students have told me that they wished they stayed in DP, because as someone posted earlier, everyone in DP becomes a family. They see each other so often that they can't help but become uber close friends, even if they do annoy each other occasionally.
Back to strength of AP courses as opposed to IB courses, though....at my school, AP math and science classes are far better than the equivalent IB classes with the possible exception of HL Chem. In fact, we haven't had HL Math/Physics classes for YEARS now, just because pretty much no one in DP either wanted or had enough intelligence (xD) to take those. But yes, the Humanities courses sound much more in-depth and time-consuming. That's why next year I'm planning on taking Business and Management instead of History! xD The only history class I have ever liked is the one I'm currently in, and that's only because of the teacher's personality, certainly not because of the curriculum.
If you're still debating whether or not to continue with DP or stick with AP, I would say that one of the key differences is that AP lets you self-select which courses/exams to take based on your own strengths, while IB forces you to commit to an entire spectrum of studies. Also, I think AP is more convenient for students, because not only do YOU get to choose what to take, but also, you don't have to be in the classes themselves to take the exams. That REALLY helps with class scheduling. And then there's DP, where to take the exam you MUST have been in the class, and where you have six required classes, which really constrains your schedule.
Some really crazy people do take both, though. I know this one guy who took DP last year along with all three main AP science exams (most people don't take APES seriously)...how he escaped senioritis I have no idea, but he managed somehow. xD
Oh yeah, and then the people who are advanced enough in math have to take either AP Stats or AP Calc or both their sophomore year (yay....) because my school does the SL Math class REALLY weird. :/
Ok wow, that was a really long post. xD Sorry! But you have to make your first post count, right?