I have seen some really interesting network partitions between SoftLayer data centers. The scenarios I saw were actually very frustrating because these weren't complete partitions (in the CAP theory sense), but just really high latency between data centers that was very sporadic. The CAP theorem addresses the situation where there is 100% packet loss both ways, but you can get "decreased availability" and "decreased consistency" with high latency. In other words, if you plan on traversing the WAN with your system, your system should take into account the high latency situation as well as classical split brain.

P.S.: at some point we stopped having these issues and overall I think SoftLayer is a great provider, at least for their bare metal offerings.