So I've taken the UP 4 times since it opened. Agree with PP's comments about lack of signs - but once you've done it, it's really easy. Certainly that doesn't help the first time user.

I like it and will take it again except for
- early morning cross boarder flights at 7 am where the 5.30 departure time would be cutting it too close, and cab is the faster option at that hour with no traffic
- late night arrivals when traffic is not an issue, I have luggage and convenience is more important, also with more than one person traveling

It's a great option when
- leaving from the office as I can walk to Union instead of sitting 20 min+ in the cab just to get to the Gardiner
- peak traffic hours in general
- bad weather
- with little luggage in combination with the TTC to get home
- with more more luggage in combination with a 12$ cab ride to/from home

What has repeatedly annoyed me is the attitude of the cab drivers. I get that it sucks for them that they don't get the 60$ rides any longer. However, this shouldn't be the passenger's problem.

One time when I got off at Union, two other cabbies were offloading zone and they were yelling at each other. It was difficult for me to get out and through with my luggage. I'm a passenger and don't care about their drama, so didn't appreciate being put in the middle of this.

Three times when I arrived at Union and went to Front Street to catch a cab, they were all lined up, but lots of cabs sitting empty. Every time, there was a discussion with various drivers until I finally found someone who was willing to take me. Of course I understand that it sucks if you wait a long time and then get a trip that's just over 10$ - I would nevertheless think that this will be true for most travelers. People with a 25$+ cab fare from Union will not bother with the UP/cab combination but take a cab right away unless maybe in peak traffic hours. One guy even yelled at me and another tourist woman who wanted to go to a nearby hotel. Great way to greet visitors - not.

Honestly, way too much yelling for my taste. I don't have yelling in neither my private nor my working life and I don't want to deal with cabbies who can't behave.
Probably next time I will just walk a bit further and stop a passing cab on the street to avoid this altogether, but passengers really shouldn't have to do this.

Then, if you don't want to pay with cash, you get sighs. None of this nonsense is suitable for (out of town) business travelers who I believe make up a significant share of the target group. Especially the expense type people will insist on charging to their Corporate card and beware if that's an Amex one.