I recently discovered in CRM 2011 that it is possible to have security roles with the same name in a Business Unit.
For example, imagine a simple business unit scenario where the root business unit is called BU1 and there is one child business unit, BU2.
Create a security role in BU1 called Manager. The Manager role will also be available in BU2 as an inherited role. If you try to create a role called Manager in BU2, the application throws an error, Role Error - The role already exists.
Now create a role called ManagerBU2 in BU2 and then create a role called Manager BU2 in BU1. What happens? Well, the application does not throw an error. But there are now two roles with the same name, Manager BU2, in BU2.
I don't know whether this is an error or expected behaviour but it does seem odd that the application does try to prevent roles with the same name in one situation but then allows it to happen in another.