I haven't used FBSL, but that sounds very much like the story with many IDEs by the time they reach full maturity.
Like you, Mike, my programs tend to be composed of lots of reusable chunks of code that are arranged by purpose.
With some big, multi purpose code, I will even use #IF NOT([variable]) to exclude sub-functions that don't need to be included.
I do like the idea of mutiple windows into a large file, but I have never used it (and don't know wheter I ever would, now that my habits are pretty set).