I have worked on 100 plus IPO's, not a huge number, but more than a few. Of the systems I have programmed I have had no major issues, but I have learned how to avoid a few.
The systems others have programmed, I have helped with on here, or elsewhere looking through the configs has always shown some programming errors. The size, as well as the quantity of errors can either cause issues. Even Avaya does not always catch all the programming errors, as I know from having sent CFG's to them early on in working with the IPO when I had systems I needed help troubleshooting.
Also, the book is very vague, does not spell out how to do everything, and therefore in many situations I can think of 10 different ways to accomplish something. For instance, time profiles in the IPO, or schedules in the VMPRO, which should you use? Now of the ten ways I mentioned, 7 suck in performance, the remaining three combined have less issues than the previously mentioned 7. The third has an issue once a week, the second has an issue once a month, the first has not had an issue reported. None of these I mention have anything programmed in a way that the book says you can not do things, but some ways are still better than others.
Of the ones which I seem to not be able to fix the issue, 4 needed a PB, the rest needed either a new piece of hardware, or downgrading the IPO, and then re-upgrading it fixed it. Other issues were sub-standard VMPRO servers, or application servers being used, etc. All 4 which needed a PB were very taxed systems running advanced applications, not your simple systems, ones with CCC, IMS, etc, and a unique probably not run into situation in the trials.