@Bruce Ordway
Interesting comments. Sounds like there was a big shift away from *nix to Windows
However you seem to be saying the *bigger* issue is the limited (nonexistent?) customization allowed by the package. Would you have been OK if it was a .Net system with the source code available?
The backup issue with *all* customization is the extent to which they will preserved when you *upgrade* the package. Other posters have described situations when the package radically changes (making a fair portion of their mods redundant) or where the the package has poor support for this and require applying the changes to the next generation by hand.
I believe there are *very* few commercial businesses (if any) which rate a completely bespoke system (usually interfaced to an accounts package) in the way that systems a decade ago might be built. However I also believe different ERP systems favor specific types of companies or market sectors. The better the fit to xx Corps business the lower the customization
Just my $0.02.