We are using the technique with connection pooling (although a WinForms app) for user/application context information required for logging purposes (used in triggers).  By always setting the CONTEXT_INFO as part of our connection logic, we do not have to worry about "leftovers" from previous users.  But in any case, I believe the connection reset that takes place when reusing a connection in the pool clears the previous user's CONTEXT_INFO (but you should verify this yourself).