Multiple users logging on with same ID

I have a question regarding multiple users logging into informix via inet with the same user id. What type of problems can this cause. My concern is what happens when page level locking is implemented and one user is updating data at the same time another user with the same id is updating the same data. Are their id threads considered the same in informix? Or are they given a different id thread since they are logged on as a different session? Will this cause conflict? Thanks pstuehl@sears.com