Currently more than half the Widows I play against are obvious XIM users. Clicking on heads instead of moving thumbsticks. This gives a clear advantage with the character over people who are not using special gadgets to gain an advantage over players. While this is an issue with all precision aim heroes, it is by far the most prevalent and advantageous to Widows.
Thing is things have gotten so bad that players often assume that if a Widow player is performing above a certain level they must be using a XIM. Good players should not have to live under a cloud of suspicion. However it will be unavoidable until something is done about it.