One thing I've seen is that when you're first learning a langauge and pick up bad habits, they can be really hard to break. I've heard lots of students talk about the problem this causes when interviewing, especially early on. Additionally, for languages like Python, where there is loads of (often excellent) support online it can be confusing/frustrating to have a class teach one method and find answers which are mostly unrelated.
That said, I agree with what was said. Scheme is pretty amazing :)