"hopefully, the entire enterprise will be looking at the same number calculated in the same way at a given time"

Sounds great in theory, but it never works out in real life. I've found that the biggest difficulties with DW are emotional. When you bring data sources from different places, something is always wrong. Plus, you look under all the rocks and find really nasty stuff.

Finally, there is never just one version of the truth. Again, sounds nice in theory, but there is a reason why organizations break down into silos.