I have always seen performance issues when we use various instances for Oracle DB across different continents? Is that not a problem for SFDC? It seems it all runs on the same instance? Does every app for a say a company A run on the same instance or is it one app per instance?
Every app run on same instance but not same server. There are lot of servers for given instance also when you are using salesforce you need a thorough performance considerations in your application and avoid low performance queries. This is part of 501.