Time will tell.
I am, obviously, only one businessman/business traveller but what I look for in my journey from or too an aiport is the best combination of speed and certainty.
Currently, cabs in toronto do not beat the proposed rail service on either.
The trip from my office to Pearson can take anywhere from 30 minutes (not sure who suggested 20 minutes in non-rush but I can assure you it has never happened for me.....geez from the corner of King and University it takes anywhere from 7 - 10 minutes (or more) to get on the Gardiner.....so how a cab would get from there to the airport in 10 - 13 minutes I do not know) to 90 minutes....the reality is that I usually budget 50.
Having budgeted 50 minutes...there are two equally frustrating things that can happen.....I can get to the aiport in 30 minutes and realize that the last meeting could have continued for 20 more minutes......or I could get to the airport in 90 minutes and realize I have just spent that last 60 minutes of a 30 minute cab ride rearranging flights.
What a service like Blue 22 offers is time certainty.....I know that if I leave my office and walk to Union I will be in the airport 30 minutes later (or whatever time it is).....similarly, business people coming into town will know that if their flight lands at 8 they can/will be at Union by 8:30...and they can schedule the day accordingly......there isn't a business traveller anywhere who has not experienced that awful feeling of being stuck on some city's aiport freeway, not moving looking at other people not moving and calling a client/partner/contact and saying...."I really can't say for sure what time I will be there....hopefully you will still have time to see me....I have flown in for this you know?"
There is a myth that the only consideration amongst the suit and tie-bay street-business traveller is the cost and tax deductability of a trip from/to the airport. Time management and certainty is a big factor....if there is an easy, comfortable, reliable and predictable service it will get its share of the business traveller.
I have long said that if GO even had 30 minute service on Georgetown to Malton and an easy bus/shuttle from there into the terminal it would win some business/downtown customers as the time risk in that journey is, typically done by the time you get to the 427/401....and rail bypasses that.