Well so far I'm fortunate enough not to need a service animal, but my kitty is a huge comfort to me.
On the other hand, if we could teach them to alert us to things like: You are about to blurt out some stupid comment - DON'T DO IT or THIS IS A TERRIBLE DECISION, DO SOMETHING ELSE or DON'T LEAVE THAT THERE, PUT IT UP NOW! or DON'T FORGET TO PAY THIS BILL! - I could really use a service animal like that!