I mean, come on... you've seen SOOO many.
Well, I have to admit, I have seen and read and heard about so many failures, you begin to wonder if it really *IS* worth it.
I have seen two really successful implementations of ERP systems.
1) GRCC using Peoplesoft, with a Wonderfully Terrific DBA, that understood HOW Oracle really worked. A Data-Manager who really understood the whole data picture, 4 programmers that really knew their poop... All 4 had come from OLD VMS, switched to new epoch *NIX and now onto mixed environment including AIX, Linux, Windows, Netware, Solaris and a myriad of "VM" machines for compute nodes. And last, a set of 3 System and Network Analysts that really could be counted on to snatch projects away from defeat due to bad installation guidelines shipped from the Myriad Vendors, mistakes by said vendors and so on...
2) The company (JWI) decided to implement the modules as they needed to. If anything needed updating, it went on the new system, they developed a bridge setup to miror all the needed data for the old system to still make reports. But they forced everyone to do all input and mainteance on the new system. Any change(enhancement or simplifing) to any report was mandated on the new system. Within 2 years they were on the New System with Zero problems during that cutover. Believe it or not they still have to old system up and running but in a virtual machine and read only... with current data. Paid to have it modified to work with the new data. There are a couple of terminals out in the wharehouse that really only need "lookup" capacity. Since the old system is running and booting from CD... eh.