Yes, I have.
Both were SAP rollouts. One was for a company I worked for and the implementation process took 7 years total. But hardly a hitch.
The other was ExxonMobile’s implementation. Which I studied and continue to cite as a best practice scenario. Took less than two years, but involved keeping SAP vanilla and being utterly draconian about ANY customization. Where a customization was requested, they really forces the business owners to change themselves to fir the system.
There was a third success at this scale as well, mostly custom build with pen source. 10 year incremental effort, still underway. But still successful.
There were three utter failures as well. All big bang style implementations. One was a disaster of an ERP (PeopleSoft) implementation that helped destroy a 16,000 person company. Another straight custom dev for a very complex business model and the third a hybrid Buy/custom build, also for a very complex model, that tried to integrate 20+ COTS products.
It all really boils down to Gall’s Law,
7, 10 year software implementations a success? That speaks for itself. But that’s the perspective of the implementers who continue to milk that cow, and not the customers who have committed to feed that animal and can’t back off. I have seen it too, have seen the cynicism and opportunism of the consultants, have seen good vice presidents of companies fired and replaced by none other than these consultants, and have seen one company go under as a result of the cynicism and opportunism of software sellers.