One of the major irritations to multinational companies attempting to manage their employees through a single database is the inability to outsource payroll to a single provider. Instead, if the MNC is in 20 countries, it's likely they will have a centralized PeopleSoft or SAP HRMS with 15 or so interfaces to multiple payroll vendors. Managing all these interfaces is difficult and getting clean payroll data back in like formats for reporting purposes is all but impossible. (I'd like to hear more on this topic from you guys in Asia/Pac/Aus and EU).
Today, Ceridian announced some global capabilities. I'm actually a little skeptical as Ceridian hasn't been able to connect their own domsetic systems well, so the chances that they can do it globally are even less likely. However, Ceridian seems to have a centralized outsourcing center in London to handle global payrolls. I'm not sure what platform they are running on.
In contrast, ADP has been doing global payrolls for ages. They own the largest payroll outsourcers in Europe, and have a huge footprint in Asia/pac as well. If you want global outsourced payroll on a single platform, they are using SAP as the gross to net engine and they interface to their local ADP backbone for stuff like taxes.
I'm sure the major HRO players have capabilities as well, but I haven't researched these.