Admittedly, a controversial title, but stay with me. In the end you will see that this is a natural outcome of BPM being successful, and not any kind of flaw. I discussed this concept with many people at the BPM 2010 conference. The response was often surprise.
It is really quite simple: in the workplace there is a mix of routine work and knowledge work. Routine work is repeatable and predictable in pattern. Knowledge work, however, is different every time and makes us think hard about what to do for this particular situation. Routine work can more easily be automated with a BPMS. Therefor, the mixture of work is shifting toward having less routine work, and more knowledge work. Automate work never results people becoming idle. Business being always competitive, people are expected to keep busy with whatever most needs to be done, and that is increasingly knowledge work.
This is an irony with all automation in general, not just BPM. It is always easiest to automate the easy work first, leaving a greater concentration of harder work. Fritz Machlup came to this same conclusion in his study of the trends of knowledge work:
On balance, the end effect of both mechanization and automation may be found to lie in the demand for more highly skilled labor, manual and mental. … The changing employment pattern indicates a continuing movement from manual to mental, from less to more highly skilled labor. 
This should not be surprising. Offices no longer have “typing pools”. There are no longer accounting clerks who spend all day adding up numbers. These kinds of easy jobs have been largely eliminated. Instead those people today would have to focus on more highly skilled uses of their time.
While knowledge work is more valuable than routine work, it is also more stressful. It is by nature more creative; there is less clear guidance on exactly what must be done; there is a greater risk of making a mistake. It is precisely because the work is hard to automate, that workers have to spend more intellectual effort while doing the work. One way to say this is that workers are increasingly becoming more like executives. Perhaps in the future everybody will be an executive.
The only surprise is that this increase in stress is not intuitive. Most would think that if you automate something, then the lives of everyone will be easier. I recently re-read Viktor Frankl’s classic “Man’s Search for Meaning” and noted in an unimportant passage this quote: “… progressive automation will probably lead to an enormous increase in the leisure hours available to the average worker.” Nothing could be further from the truth, yet this was the common view of automation in the 1950’s. I always remember the 1960’s Jetsons cartoon set in the far future where George Jetson’s job consisted of pressing a single large button on his desk, because everything else was automated. These visions of the future seem natural, but ignore the competitive effects of economics. Automation allows the organization to be far more productive, because a single person can do far more work than before, yet that person need to do only the part of the work that is hard to automate. In short, automation produces a shift to require more highly skilled labor.
I see this trend as an indication of the success of BPM. BPM (all types) has been very successful in automating work, and making organizations more productive than before. But the work remaining after automation is more stressful on the employees. Yet, we have no choice. An organization can not choose to avoid such automation. A company that decided to return those routine tasks to workers would find itself at a competitive disadvantage, with higher costing products. We must automate, and we must accept that the workplace will become more challenging on the average.
There is a bright spot in all this: while routine work is easier, it is often more boring and unsatisfying. By automating the dull, repetitive, boring work, the remaining work tends to be more satisfying and meaningful on the average.
 While Peter Drucker is known for coining the term knowledge worker, Fritz Machlup is often recognized as the person to do the most to define and rigorously study it. This quote comes from “The Production and Distribution of Knowledge in the United States“, Princeton University Press, and I found this article republished in “The Rise of the Knowlege Worker” by James W Cortada.
 as a side note, the future has turned out strangely similar to that anticipated by The Jetsons: I have 101 buttons on my desk (keyboard) and I do nothing but press them repeatedly all day long. 🙂