I was looking at this from the angle of breakages, and I remember following some of the P5P threads when things were removed that caused breakages on CPAN. For modules that are high upstream on the CPAN River, patches were submitted, and for other packages, bugs were filed on RT.

Right -- all that to say, there have been some minor changes, but p5p have been quite good about testing and making fixes as they are required, in order that there's the least amount of surprise when the new version of Perl is released.

Also -- funny you mentioned study, as I was going to use that as my example function, then decided it was a little too obscure, and replaced it with split. I'm aware of it, but never had a regex complex enough to wonder if study might have helped. Also, I'm the kind of person who actually does read every line of a thousand page reference book, even if I only end up using 20% of the material. And study was used in a piece of Perl poetry I read, and I thought it was a cool keyword.