I have some experience with multiple institutions on the list (and I know other folks that have taken classes at more than one).
Here is my take: sdn is dominated by people from CA (read: "ASIANS"). As a race, you'll find more whiners among Asians. There is a lot of pressure from folks to get all As and become doctors. As a result their is a perceived notion that UC Berkeley is hard. As someone that has taken classes at both their campus with their undergrads and through their extension school, this is pretty exaggerated. I've NEVER in my life met as many people complain about how "hard" classes are in my life. Not when I took classes at Harvard, Brown, Northeastern etc.
As far as REAL difficulty is concerned, UVA is actually much harder. That said, it really comes down to prof/class. Each of these institutions have easier/harder classes. U of MI is no cake walk either. Some of the other UCs aren't really in the same ballpark as these other institutions (UCLA and UCSD... UCSF doesn't have an undergrad program). I don't know anything about UNC Chapel Hill so I can't fairly comment, but I don't believe its in a similar ballpark (but this is based on my perception of it).