Maybe because I had a complete semester of multiprogramming in the uni, I see almost trivial to work in such environments, and cannot comprehend why is so much mystic and voodo. Actually is pretty simple.
I feel like it's not terribly hard to write something that more or less works using mutexes and the like, but I find it exceedingly hard to debug. You're at the mercy of timing and the scheduler, meaning that often just throwing a breakpoint and stepping through isn't as easy as it would be with a sequential program.
I feel like with a queue or messaging abstraction, it can be easier to debug. Generally your actual work is being done on a single thread, meaning that traditional debugging tools work fine, and as I've said in sibling comments, I also just think it's easier to reason about what's going on.
